• Pressing Return is the same as clicking OK, Yes, or Continue
• Pressing Esc is the same as clicking Cancel.
• ⌘-A selects everything in the current window.
• ⌘-C copies the selected text or image to the Clipboard.
• ⌘-X copies the selected text or image and stores it on the Clipboard and then deletes it from […]

To quit “frozen” applications on your Mac without having to shut the cmputer  down click on the Apple menu and select “Force Quit”.  This forces a pop-up window to appear and you will see the trouble application listed in red.  The keyboard command for this is holding down the Command-option-esc keys at the same time.

Check out this Apple support page for some mac basics.
Mac 101: Get started with the Mac

First, dim the display. Dimming your display increases battery time between charges
Second, go to System Preferences -> Energy Saver […]