The Dock can seem like an annoyance from time to time, but there are lots of things you can do to make it more useful. Here is a basic tutorial along with some shortcuts that will have you singing its praises in no time!
1) The vertical line: The line that separates the Trash and your applications is a good thing to note—for one thing, you can click and hold on this line to resize your dock on the fly, either dragging up to make it larger or down to make it smaller. Additionally, you can put files and folders on the right side of it (right next to the Trash) for easy shortcuts. Though it seems to be a constant struggle, I like to keep my Desktop free of clutter, and this dock tidbit seems to do the trick. For instance, I have created a shortcut to my Applications folder and my Documents folder in there, where I can access them really quickly.
2) Dragging to/right-clicking on your icons: A really easy way to open a file in the application of your choice is to drag the file right on top of the application’s icon in the dock. (It’s also a great way to see which apps will recognize your file if you’re unsure.) By right-clicking (Ctrl+clicking on a one-button mouse) on your items in the dock, you will bring up a nice contextual menu that gives you multiple options and/or shortcuts. For example, right-clicking on Mail gives me the option to compose a new message straight from the dock! Also, if you have put folders in your dock, right-clicking on them will give you the option to pick the exact file you’re looking for, right then.
3) Hiding applications, or even the Dock itself: The keyboard shortcut to hide an application is Command/Apple-H, as well as from the contextual menu once you’ve right-clicked on it. I do this a lot, since I like to keep my applications running but I don’t always like to see them. Similarly, if you don’t want to see the Dock but you hesitate to hide it all the time, you can do so on the fly with Option-Command/Apple-D.
4) The floating Dock: My favorite, though, has to be the floating dock—by clicking Command/Apple-Tab, you will see a slightly transparent, “floating” version of the applications that are open on your computer. If you hold the Command/Apple key down and then press Tab repeatedly, it will scroll through the list. Though this trick is not necessarily a function of the Dock itself, it is a great way to preview what you have open and quit programs right from there. To quit, keep holding the Command key down and switch your other finger from the Tab key to the Q. So quick!
By the way, the images above are of my dock (left + right side), with many changed icons. More on that later…
By the way (x2), the icon of the scissors is a cool application called Grab, which you can use to take screenshots like those…