The Chorus effect adds thickness and warmth to the signal. The output signal is a mix of the input signal and a delayed copy of it. The delay time is modulated.
The Delay knob sets the average delay time. The Speed and Depth knobs control the modulation.
The Mix knob sets the dry/wet ratio (0% being dry only, 100% being wet only). If you use an Effect Return for adding Chorus set Mix to 100%. If used as an insert effect Mix will usually be set below 50%.
The No Color button removes the coloration traditionally associated with Chorus effects. This works best with Mix values of approximately 50%.
If the Stereo button is active a stereo chorus effect will be applied to mono signals (this is usually the effect you're looking for). The Reverse St. button is identical, except that the signal will 'spin' in opposite direction.