From Mac Guides
The Dock is an interactive list of all the applications currently running in Mac OS X. It also displays certain other applications, files, folders, minimized windows and the Trash. It appears on the bottom or side of the Mac display at all times (except when hidden).
The Dock can also be customized to include any applications, files and folders. Currently running applications are differentiated from non-running applications by a small black triangle pointing from the edge of the monitor to the application's icon.
To add an item to the Dock, simply drag its icon onto the Dock. Applications must be dragged to the left or above the line dividing the applications from the trash; all other items must be to the right or below it.
Note that this process does not physically copy the item -- the item remains in its original location.
To remove from the Dock, drag the icon away from the Dock and let it go. It will disappear in a very satisfying poof of smoke (again, this does not remove the item from your computer; it remains in its original location).
You can rearrange items on the Dock by dragging them to their new location.
You can edit Dock settings by clicking on the Dock icon in System Preferences, by using the Dock submenu in the Apple menu, or by control-clicking on the divider in the Dock. Settings include the location of the Dock, whether it hides automatically, whether it magnifies the content under the mouse, and what size it is. If the Dock is hidden, you can access it by moving your mouse to the side of the screen where it is located.
Another way to quickly resize the Dock is to click and hold on the divider between the applications and the trash/documents, and drag up or down. When holding down the shift key while clicking and holding on the divider you can quickly change the Dock's location by dragging it to the left, the right or to the bottom of the screen.
You can also quickly toggle between hiding and showing your dock by typing command-option-D.
Another way to customize the dock (in Mac OS X 10.5 only) is to change the look of it with a third party tool, such as as Panic's Candybar 3.
To run an application or open a file, click on its icon in the Dock. To access an item within a folder on the Dock, click and hold to display the folder contents. Then navigate to the file or application you want.
You can also quit, hide, or show the location of any running application by clicking and holding on its icon in the Dock, which displays a menu. If you hold down the option key while showing this menu, additional options will become available, such as Force Quit. Many applications such as iTunes offer additional functionality by clicking and holding their dock icons.
To open a file with a particular application (for example, to open a Microsoft Word Document using TextEdit), drag its icon to the application's icon in the dock. If the icon does not highlight, but you want to force the application to try to open the file anyway, hold down the command and option keys while you drag.
To delete a file, folder, or application, drag its icon to the Trash. To unmount or eject an iPod, CD, DVD, disk image, or other device, drag its icon to the trash, which will change to an eject icon.
Other Roles of the Dock
Behind the scenes, the Dock also runs several other features of Mac OS X. These include
- Minimizing windows.
- Exposé from Mac OS X 10.3 onwards.
- Dashboard from Mac OS X 10.4 onwards.
- Stacks from Mac OS X 10.5 onwards