Each effect has two modes, constant and momentary. In constant mode, the effect runs continuously, this is the default mode. In momentary mode, the effect is only activated when the buttons in the green momentary column are pressed; CRUNCH! ECHO! REVERB! etc.
There are also key commands for momentary activation:
1 = Distortion
2 = Echo
3 = Reverb
4 = Chorus
5 = Pitchshift
6 = Vocoder
7 = Filter