well, you plug your SM58 into it, and plug the other end into an amp, adjust the preamp, dial up a patch and your good to go. There is an on/off switch, a patch advance switch and an expression pedal for pitch shifting effects.

It is a nice bit of kit if you like that sort of thing.

It can be used to add anything from a subtle verb to voice transformations using patches like "Wizard", "chipmunk" and "monster"

I had one but never used it. It also wont supply phantom power for condenser mics.