Ctrl + A = Select All. Selects all contents of the active window. It is useful when copying large amounts of data.
Ctrl + C = Copy / Ctrl + X = Cut. Copies the contents of the selected area to the clipboard.
Ctrl + V = Paste. Pastes the contents stored in the clipboard.
Ctrl + Z = Undo. Goes back a step. Useful when mistakes are made.
Ctrl + S = Save. Saves changes to the active file.
Ctrl + P = Print. For printing the active document.
Alt + Tab = Switch windows. Switch to another window or application.
Alt + F4 = Quit / Exit. Exit / Close the active application.
F11 = Fullscreen. The F11 function key is often used in many applications to maximize to full screen.