Top Boost Vox amps have different tone controls than other amps. First, the cut control - think of it as a presence or treble reduction control, with it turned all the way to the left it's off and the amp is it's brightest, with it to right the amp is the darkest. Set it all the way to the left as you adjust the other controls, then adjust the cut to the room you're playing in.
The master volume should be all the way up if you want the cleanest sounds the amp will make, and the amp will sound buzzy / farty with the master below about 25%. For the dirtiest possible sound, turn the main volume control to 100% then reduce the master to the volume you want. Realize that this amp will never make loud clean sounds at rock gig volume, it's a dirty amp at gig volume, you need to mike it for rock gigs if you want loud clean sounds. For the cleanest possible early Beatles type sounds, master at 100%, main volume at about 1/3, cut at zero (maximum treble), treble and bass controls somewhere in the middle, probably the treble would be higher. For Tom Petty type semidirty sounds, master at about 1/3, main volume at about 60-75%.
The tone controls are interactive - start with them both at 50% (straight up) and adjust one at a time, noting what they do. Don't be afraid to have the bass at 25% and the treble at 75%, or vice versa. You'll probably never use it with the bass at zero and the treble at 100%, but listen to it that way and decide.