Congratulations ! All the Rockman stuff is so cheap used, it's almost a crime not to buy it. You get great quality for little money.
The effects send (or pre-amp out) of your amp goes to the input of the chorus. The mono out goes to the effects return (or power amp in) of your amp.
All the other things there are for switching the unit functions and bypassing and another output for use in stereo setups. Some of them are really sweet, such as the "sweep stop" function. It simply "freezes" the sound of your chorus.

If you want to be able to be able to turn this bugger off, connect a basic footswitch to the bypass input on the rear.
If you could give me some more deteails of your setup, I might be able to give you some more pointers on how to get the most out of this little bugger.
Let me know what you think of the sound. Even mono, I'd say this thing is pretty wide.