The OS X dock is invaluable to any Mac user. It's a dedicated spot for you to place shortcuts to apps, files, and folders that you access on a regular basis. Besides just clicking on an icon in your dock to launch it, there are a variety of key combinations you can use to extend the utility of your dock.
Command-Option-D to hide/show the dock
Press Command-Option-D to hide or show the dock. You can accomplish the same task by choosing dock from the Apple menu and then Turn Hiding On or Turn Hiding Off from the submenu. You can also set the dock to automatically hide or show in the dock Preferences.
Click on a dock item to open it
Clicking on a dock item brings the item forward, or opens it if it is not already open. It also opens minimized windows.
Shift-click on a dock item to slowly open it (minimized windows only)
This will open a minimized window in slow motion. You can also minimize a window in slow motion by pressing Shift while minimizing it.
Command-click on a dock item to locate the item in Finder
Press Command and then clicking on a dock item will reveal the original item in the Finder.
Control-click on a dock item to view contextual menu
Control-click on a dock item reveals the contextual menu for that item. What you see in the contextual menu varies based on the application or file. You can also long press or use a two-finger press on a dock item to reveal the contextual menu.
Use Option to change items in the contextual menu
Pressing option when viewing the contextual menu allows you to replace "Quit" with "Force Quit" and "Hide" with "Hide Others." The "Hide" option will hide the app on the screen, while "Hide Others" will hide all other apps. It's very useful when you are working with multiple windows and want to focus on one.
Command-Option-click on a dock item to hide other open items
Command-Option-click will bring the app that you clicked on to the front and hides all other open items. It's very useful when you are working with multiple windows and want to focus on one.
Control-click on the dock separator to access dock preferences
Press control and then click on the dock separator to reveal the dock preferences. There you can turn magnification and hiding on or off, change the position of the dock on screen, and change the minimization effect. You can also use a two-finger press on the dock instead of control-click to access the dock preferences.
Shift-drag on the dock separator to move it
Press shift and then hover your mouse over the dock separator. When the dock arrow appears, you can drag your mouse to any side of your screen to move the dock to a new position (left, bottom, right).
Option-drag on the dock separator to adjust its size in pre-set increments
Press option and then hover your mouse over the dock separator. When the dock arrow appears, you can click and hold and then use a pinch gesture to adjust the size of the dock. Using the option key sets the dock to common icon sizes (128 by 128, 64 by 64, 32 by 32, 16 by 16). You can also adjust the dock to a custom size by clicking and holding on the dock separator and then using a pinch gesture to adjust the size.
Drag a file to an application's dock icon to open it
In Finder, you can select a file and drag it to a dock icon to open it. You can only drop the file onto an app that supports that file type.
Command-drag a file to an application's dock icon to open it
In Finder, you can select a file and use command-option-drag to drag the file to a dock icon. OS X will attempt to open the file with the application you selected, regardless of file type or what application the file is associated with (if any). The application may or may not be able to open the file.
Command-drag a dock item from the dock to another location
Select command, then click and drag a dock item to another location in Finder. This allows you to copy a dock item to another location without removing it from the dock. This key combo is handy if you have a folder in your dock and you want to move the contents to another folder on your Mac.
Command-drag an item to the dock to put it into a folder
When you drag items to the dock, sometimes it will move (slide) existing dock items to make room. If you want to drag an item to a folder on the dock, for example, you should select command before you select the file you want to drag to the dock. This command-drag option will allow you to add a file to a folder without accidentally shifting other dock items.