Mac OS Folder Structure, Continued
When you open up the Finder – the double-smiley face icon that’s always to the leftmost of the dock – you are presented with the standard Finder Window, and if it’s the first time you’ve opened it, there are some basic elements there by default. A lot of these are just shortcuts to some of the places on your computer we talked about previously, but usually what I find happens is this: People think that these “shortcuts” they see are really the things themselves. Then they accidentally remove the shortcut at some point, and they think all is lost. All is not! On this page, I aim to show you that in actuality, nothing has moved except the shortcut icon itself, and I’ll even show you how to put some of the harder-to-find ones back in place.
In the above picture, you see my Finder Window (click for larger version). The Finder is the window to your files & your filesystem, and is divided up into a few different parts. The main portion is dedicated to showing you the files & folders wherever you are currently. For instance, in this picture, I’m at the Applications Folder (as indicated by the title of the window at the top), and I am viewing all my applications. To the left of the main portion is the Sidebar, and it’s the sidebar that I find usually leads to confusion with new users. The sidebar is divided into two sections, with the top being dedicated to “drives” such as your hard disk, “Media” such as CD’s you put in, and Networks your computer is linked to. The bottom half is reserved for shortcuts that you define. In the basic overview of the Finder, I showed how to create a shortcut by dragging any file or folder to the sidebar, and it would create a shortcut to there.
The thing to remember is it’s just a shortcut you’re creating, a link to the actual item you placed there, which still resides at the original location. This is a point of confusion, so let me give an example. In the first pic, you see a list of shortcuts next to the main portion. Now in the picture below, I have added a shortcut to my “Aperture” application. However, I didn’t move the application to the sidebar, I merely created a simple shortcut, so next time I need to use Aperture I can simply click the sidebar link instead of trying to navigate all the way to the actual location of the program. You can see here that Aperture is indeed still in the Main Applications folder I’m viewing; it’s even highlighted for show!
SIDEBAR ITEM LOCATIONS ON THE SYSTEM HARD DISK
Often what I see happen is that people will accidentally drag off the shortcut icon from the sidebar for one of the pre-installed locations or folders, and then think that that folder is gone. Such is not the case, as we have just seen that these icons are actually just shortcuts to the actual items. So then we need to know where the folders/files are actually located in order to put the shortcuts back on the sidebar for easier navigation.
The Documents Folder that you see is found by navigating from the top level (The Macintosh HD usually) by clicking on the appropriate icon on the top of the sidebar (either the computer icon or the HD icon), then going down to your own user folder by
Once you’ve reached your own User Folder, you probably see that the sidebar for the most part was just filled with links to folders at the top level of your own folder. Pictures, Movies, Music, Desktop, they are all here by default, and returning here is the best way to re-add the links to your sidebar if you accidentally drag them off and they *poof* away.
TOP OF THE SIDEBAR: REPLACING ICONS TO TOP-LEVEL ITEMS
In the example above, we began our navigation by clicking either the Computer Icon or the Hard Disk (HD) Icon at the top of the sidebar as top-level starting points to navigate down to our own user folder. Well it is possible to drag off the shortcuts to these top-level shortcuts as well, which could pose issues for graphical navigation above your own folder.
However, there’s an easy fix for those as well. If you go to the Finder’s Application Preferences (as discussed here), you’ll see that one of the tabs in the Preferences for the Finder is “Sidebar.”
Recap of your Finder and your File System Hierarchy
So now you’ve played with your Finder some, and now hopefully the Icons and their interplay make a little more sense. You know you can drag files & folders to the Sidebar to make shortcuts to them, and you know you can selectively activate & deactivate items from the top half as well, which is useful if you accidentally drag off an icon from it.
But maybe you’re still a little leery over what each icon represents in relation to the hierarchy we spoke about. If so, here’s a quick visual correlating some of the components in the Finder & Sidebar to the hierarchical view from earlier. Click for larger, higher-res versions to open in a new window.
In the following couple of pics, the Finder is viewing the User Folder, as is evidenced by the fact that the Sidebar's shortcut icon is highlighted. There are arrows pointing from the hierarchical graphic to what shortcut leads to it in the Sidebar, as well as an arrow pointing to that same folder as seen in the finder. So you can see the hierarchy exists in a way that you can interact with.
When you log on to your account, you’re taken to your Desktop of your User Folder. All of your documents & files are going to be contained within this User Folder. When you access applications, you’re reaching into a folder above your own account level to do so. The “Applications” folder is located near the top of the hierarchy, allowing all the users on the computer to be able to access it as needed for work & play.
When in doubt, there’s a quick & dirty way to see things in a sort of “hierarchical view.” At the top of the Finder Windows you’ll see an icon that looks like this: 
This allows you to select different views. By default it’s on “Icon View,” making all your icons big and easy to see. However, if you choose the middle button, or “List View,” you can see how things are related to one another in the hierarchy. For instance, if you click on your HD Icon in the Sidebar and select List View, you’ll be able to see a view like this:
By clicking once on the little black triangles, you can open them up to show what’s in each folder location, with sub-items nested underneath. Those black triangles are called “Disclosure Triangles,” as they allow you to disclose information about what’s inside a particular folder at will. If you continue to do that, you can end up with a view like the following, that shows where your files & folders are relative to the rest of the system:
I hope this helps clear up some confusion regarding the file system. It’s not that complicated, it’s usually just that no one is ever taught this; you get a computer and turn it on, and what you see is what you get, and that’s all you know. However, I think it pays to be aware of your file structure and where you are relative to everything else. Even if you don’t actively use all the places mentioned – I surely don’t – it helps demystify the experience, and can help make using the computer that much less of a worry.
Addendum
With the eminent release of Mac OS X 10.5 “Leopard” this coming week, the Finder sidebar will (finally!) change. Though it will not lose any of the mentioned functionality, some of the things will move slightly and be referred to slightly different. In the picture below, you see what the new Finder will look like. It bears a striking resemblance to iTunes now, but the old “Top” of the sidebar is still present as is the “bottom” of the sidebar. The new “top” is called “Devices,” referring to the fact that they are actual media usually (Hard Disks, CDs, etc). The new “bottom” will be referred to as “places,” meaning “places that you want to navigate to quickly, often.” 
Again, it’s basically the same thing, but organized a little different/better, and with a slightly updated look to it. If you’re on 10.5 as you read this, then more than likely none of the previous article looked familiar until about 10 seconds ago. However, for those still on 10.4 or below (the majority of you), hopefully it all looks very familiar and now makes a little more sense.