Release mode controls what happens when the shutter is released.

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

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

Continuous high speed
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.

Qc (quiet continuous) shutter-release
The camera takes photographs while the shutterrelease button is pressed; camera noise is reduced.

Self-timer
Take pictures with the self-timer.

Mirror up
Raise the mirror before taking photographs.