Switches on the preamp..

They don't sound silly at all, so all is cool (don't ask - stay ignorant, right?) Here's a non-tech answer from a non-techie.

Presence - brings out the upper harmonic content. Compare with turning up your treble control. Notice how the Presence gives you a glassier, sharper, different, high end?

Gain - Try comparing this control with your volume. It regulates/matches the amount/strength of your signal from the instrument to the amp. This has to be balanced with your volume control(s) to get the strongest signal possible with the least amount of noise. If your profile was filled out (a necessity to get intelligent answers usually) I might know if your amp has a clip LED and we could talk about gain staging your amp.

Some people mistakenly think Gain is another volume control by another name - it's not.

EQ will allow you to tailor your sound/frequency ranges to use different rooms to their best advantage. For instance, if you are playing in a room where you have trouble being heard with a loud guitarist or keyboardist, boosting the mid-frequencies of your EQ's mid-freq's usually allows your sound to cut through. Without knowing whether your amp has graphic EQ, parametric, both, et al, it's tough to address your specific situation.

But, it's safe to say most bassists these days favor "the smile" - the low and high freq's are boosted up and the mid freq's are dropped down, forming a "smile" or "U" shape on a graphic equalizer.