What are these buttons on a guitar amp?

The chorus, phaser, tremolo are all different types of effects, just play around with em and you'll learn if you like them or not. The reverb effect is kinda cool. It makes it sound like your playing in a much larger room like at a concert or something. The more you turn the knob for any given effect usually changes the presence of said effect. The more you turn it the more noticeable the gain is what gives it the distortion, less of a clean sound and more of what you here in rock and metal, my motto is the more gain the better! :). Id put the treble about 3/4 the way up. the mids about half, and the bass about 3/4. You can experiment and see what you like. Hope this helps!