The Enable buttons turn a module on and off. Off means the effect is entirely bypassed. When a module is turned off it is covered by a "hatch". You can click on the hatch to turn it on.

The Big Knobs adjust the amount of each effect. At 0 % the module is completely bypassed. If a module is turned off (hatched) you can simply click/move the big knob to turn it on (no need to click the Enable button first).