In OS X (Sierra) when you double click on file's icon, as opposed to an application's icon, the default application associated with that file and its icon is then launched (executed/run) in order for it to then open the actual file and display its contents. So if you double click on a Photograph file (on its icon) the default application called Preview will launch (execute/run) in order for it to then open the actual Photograph file (i.e. Photo_001.jpg) and displays it contents (i.e. a picture of a Flower).
And the same applies if you double click on a Document file (on its icon). Its default application (i.e. Microsoft Word or Textedit) will launch (execute/run) in order for it to then open the actual Document file (i.e. Letter.docx or Research_Notes.rtf) before displaying its contents (i.e. the Letter or Research Notes).
A Shortcut Icon (or Link) is the copy icon. Its job is to know where the original file or folder is on your computer or network so that when you click or double click on that shortcut icon, depending on where the shortcut icon is (i.e. on the Desktop Screen or Dock), it knows which application file to launch or which folder to open for example. So the icon attached to a Document file is a shortcut icon. As is the icon attached to a Photograph file. The photograph file, and more precisely its icon, is associated with (linked to) the application called Preview, by default. When you double click on that shortcut icon it looks inside the APPLICATIONS folder for an application called Preview and then launches it (executes/runs it). From there the Preview application opens the actual photograph file and displays its contents.
As well as files using shortcut icons, folders use them too. For example, the FINDER sidebar uses folder shortcut icons (also known as: Folder links). The DOCUMENTS folder (folder link / shortcut icon) on the FINDER sidebar is actually a shortcut to the path name: MACHINTOSH HD >> USERS >> USER NAME >> DOCUMENTS. Look at the following Path Bar, towards the bottom of the FINDER window.
Fig 1.1 Clicking on the DOCUMENTS folder links to: MACHINTOSH HD >> USERS >> USER NAME >> DOCUMENTS
As you can see: When you click on the DOCUMENTS folder (folder link) within the FINDER sidebar you are not taken to a folder called DOCUMENTS on your Desktop Screen. You are in fact taken to the DOCUMENTS folder that resides in your USERS folder (i.e. Yoingco) which in turn resides in the USERS folder which in turn resides in the MACHINTOSH HD folder. So instead of having to double click on the MACHINTOSH HD folder, double click on the USERS sub-folder, double click on the USER NAME sub-sub-folder and then double click on the DOCUMENTS sub-sub-sub-folder all you need to do is click once on the DOCUMENTS folder link (shortcut icon) within the FINDER sidebar. And that's what a shortcut icon is all about - Making life easier.
In this first example I am going to make a shortcut icon for the Letter.docx file inside the DOCUMENTS folder. There are three main methods for creating a shortcut icon. The first method is to select (left click on) the Letter.docx file in order to make its FINDER menus available. From there you click on its FILE menu and select the MAKE ALIAS menu-item. The MAKE ALIAS menu-item is the equivalent of Windows 10 CREATE SHORTCUT menu-item.
Fig 1.2 Method 1 - Select the MAKE ALIAS menu-item from the FILE menu
With the second method you click on the Letter.docx file but this time select MAKE ALIAS from the ACTION button. So click on Letter.docx, click on the folder's ACTION button and then selects its MAKE ALIAS menu-item.
Fig 1.3 Method 2 - Select the MAKE ALIAS menu-item from the ACTION button
With the third method you right click on the Letter.docx file to bring up its Context (Options) menu and then select (left click on) the MAKE ALIAS menu-item.
Fig 1.4 Method 3 - Select the MAKE ALIAS menu-item from the Context (Options) menu
Regardless of which method you use to create the shortcut icon (Alias) you will end up with a duplicated icon for the Letter.docx file whereby it has a file name of Letter.docx alias. That file name, once the shortcut icon has been created, is ready to be edited straight away if need be. hence the RENAME edit box around it. If you like the file name Letter.docx alias then simply press the ENTER keyboard key, or click anywhere inside the DOCUMENTS folder, to keep that file name.
Fig 1.5 The shortcut icon will have the same file name as the original file but with the word ALIAS added (suffixed)
It is important to notice and distinguish here that you have only created an icon and not a duplicate/copy of the original file itself. A shortcut icon always has a tiny black arrow in its bottom-left corner, with a file name that is suffixed with the word ALIAS, so that you know it is a shortcut icon and not the original file. Furthermore, if you right click on both icons and then select their GET INFO menu-item you can compare their File Information.
Fig 1.6 Right Click on an icon and select the GET INFO menu-item to view/compare its File Information
In the example below I have the file information for the original Letter.docx file on the left and the file information for the shortcut icon (alias file) Letter.docx alias on the right. Remember - A shortcut icon is also a file in its own right. It contains path name information and other details about the original file it is a shortcut of. Its file size is normally 688 KB.
Fig 1.7 File size of Letter.docx alias (Shortcut Icon) is 688 KB
Fig 1.8 Original file size of Letter.docx is 20 KB
If you now look at the WHERE field (record/entry) for both the original file and shortcut icon file they are both stating the DOCUMENTS folder (Path Name: USERS >> YOINGCO >> DOCUMENTS) is WHERE they are located. Obviously because they are both inside the same DOCUMENTS folder at the moment. However, if you look more closely at the shortcut icon file information it has an extra field (record/entry) called ORIGINAL that states where the original file (Letter.docx) resides. Again, inside the DOCUMENTS folder. So far this is obvious because both files are in the same folder. However, that ORIGINAL field lets you know that you are looking at a shortcut icon file as opposed to an original file. As does the KIND field - It states ALIAS as the type (KIND) of file whereas the original file states Microsoft Word Document as the type (KIND) of file.
In normal circumstances you would not have both files (the shortcut icon file and the original file) in the same place simply because the idea of the shortcut icon is to shortcut to (connect with and open) a file or folder that is buried deep within your folder system, as shown in this next example. In this next example I have the Letter.docx file stored inside a folder called ORIGINAL FILES located on my network hard drive (server). I created a shortcut icon for it (as exampled above) that initially resided in the same folder (ORIGINAL FILES). However, I have since moved that shortcut icon file into the DOCUMENTS folder on my computer; Hence the following file information for both the the original file and shortcut icon file.
Fig 1.9 The shortcut icon file is on my computer
Fig 1.10 The original file is on my GoFlex Network
If you look at the Letter.docx alias shortcut icon file first (on the left) you will notice its WHERE field (record/entry) states the DOCUMENTS folder because that is where the shortcut icon is located. However, if you now look at the ORIGINAL field it states that the original file (Letter.docx) is located on my GoFlex Network hard drive (server) - Path Name: VOLUMES >> YOINGCO >> GOFLEX HOME PERSONAL >> ORIGINAL FILES. This by the way is how you find out where a file lives; by using the GET INFO menu-item and then looking at the WHERE and ORIGINAL fields for example.
If you now look at the original Letter.docx file (on the right) you will notice its WHERE field states the Path Name: VOLUMES >> YOINGCO >> GOFLEX HOME PERSONAL >> ORIGINAL FILES as its original location. Furthermore, the path name to the server is given in case you need to COPY & PASTE it and use it for whatever reason(s). Path Name (Server Address) - AFP: >> GOFLEXHOME._AFPOVERTCP._TCP.LOCAL >> YOINGCO >> GOFLEX HOME PERSONAL >> ORIGNAL FILES. VOLUMES by the way is a shortcut in itself - It actually points to a mounted disk drive on the computer called Yoingco which is basically the root/main folder for the network hard drive GoFlexHome (Network >> GoFlexHome). Ignore these technicals if you wish!!
Hopefully you can see how a shortcut icon saves time. Once you have created a shortcut icon and moved it (i.e. cut and pasted it or dragged it) on the Desktop Screen or into the DOCUMENTS folder for example it means you do not have to wade through layers of folders. In the above example; Instead of double clicking on the NETWORK folder (VOLUME / GoFlexHome), the USERS folder (YOINGCO), the Hard Drive sub-folder (GOFLEX HOME PERSONAL) and then the ORIGINAL FILES sub-sub-sub-folder, all I need to do is double click on the shortcut icon file located inside the DOCUMENTS folder. So two clicks instead of eight clicks.
If you ever come across a forgotten shortcut icon and want to know what application it is going to launch (execute/run) and/or what file it is going to open simply use the GET INFO menu-item as just exampled above. And if you need to open the folder of the original file right click on the shortcut icon file and then selects its SHOW ORIGINAL menu-item (Fig 1.11 below). In this case it will take you to the ORIGINAL FILES folder on my network hard drive (Fig 1.12).
Fig 1.11 Right Click on the shortcut icon file and then selects its SHOW ORIGINAL menu-item.....
Fig 1.12 .....to get inside the folder (location) of the original file.
Shortcut Icons are not only created as shortcut links to folders and files. They can also be created as shortcut links to websites and web pages. When you have a website or web page you like you normally add it to your web browser's list of Favourites (Bookmarks). In other words, you bookmark (or add to Favourites) that website's address or web page's address (url). However. If you want to create a shortcut icon for it on your desktop screen for example you can do so by dragging the website's or web page's icon off the web browser's Address Bar and onto your desktop screen.
So in the example below I have the TFL (Transport For London) website address inside the Safari web browser's Address Bar edit box. If I now drag its icon from the Address Bar itself onto my desktop screen a shortcut icon will be created for the TFL website.
Remember - Dragging is the technique of clicking on something and keeping the left mouse button (click) held down as you then move the mouse pointer (with that something attached to it) from A to B before releasing the left mouse button. So in this example I have clicked on the TFL website icon, kept the left mouse button held down as I then moved the mouse pointer away from the Safari web browser window (with the TFL website icon attached to the moving mouse pointer) before letting go of the left mouse button once the mouse pointer was over a blank part of the desktop screen.
Fig 1.13 Click on a website icon and keep the left mouse button held down as you move the mouse pointer
Fig 1.14 Move the mouse pointer away from the Safari web browser window, towards the desktop screen.
Fig 1.15 Release the LMB to create the TFL website shortcut icon, named Transport For London.webloc
Fig 1.16 Rename the shortcut icon, if need be, to something more meaningful like: TFL.webloc
In Figures 1.13 and 1.14 above I am dragging the TFL website icon (mouse pointer) away from the Safari web browser window and onto my desktop screen. Once the TFL website icon (mouse pointer) was over a blank part of my desktop screen (Fig 1.15) I then released the left mouse button thereby dropping the TFL website icon onto my desktop screen and creating the shortcut icon for it. The shortcut icon (file) was originally named HOME | Transport For London.webloc (Fig 1.15) but I decided to rename it to something more meaningful - TFL.webloc. Double clicking on the TFL.webloc shortcut icon will now launch (execute/run) the Safari web browser application and in turn will display the TFL website.
If you rename the shortcut icon (file) you must keep the .webloc file name extension. Deleting it will create a void file (void shortcut icon) which will not open with most, if not all, web browsers.