Well... the tuning guide roughly describes what they do.. but..

Gain: Basically this sets the rate at which the boost controller allows the boost to increase past the wastegate spring. The higher you can run it w/o overboosting/spiking, the better, but this number usually ends up pretty low for everyone.

Set Gain: This is the lowest point at which the EBC will begin to increase boost under WOT. You want this as close to your "Set" value as possible without overboosting/spiking.

Edit: And no problem You beat me to the reply button.