The option key on the Mac keyboard enhances some of the actions you can perform.
In all these tips, hold down the Option key and perform the indicated action. The Option key is usually located on the bottom row of the keyboard between the Command (Apple) key and the Control key. There is one on each side. You only need to press one of them.
Option + Click a window shut
Closes all the windows behind it.
Option + Double click an icon
The icon will open, closing the window the icon is in .
Option + Empty Trash
Deletes all files including any that are locked. Locked files normally cannot be deleted. They can be unlocked by the check box in File, Get Info.
Option + Drag a file or folder to different window
Copies the file or folder, leaving the original as is. The default without the Option Key held down is for a file or folder on the same drive to be moved.
In Word processing, use the Option Key with the Arrow Up or Arrow Down Key
Jumps to the start or end of the current paragraph.
A more comprehensive article may be found at http://en.wikipedia.org/wiki/Option_key