Release mode controls what happens when the shutter is released.

 Single frame
Camera takes one photograph each time shutter-release button is pressed.

 Continuous L
The camera takes photographs at a slow rate while the shutter-release button is pressed.

 Continuous H
The camera takes photographs at a fast rate while the shutter-release button is pressed.

 Quiet shutter release
As for single-frame, except that camera noise is reduced.

 Self-timer
Take pictures with the self-timer.