[9W Monighan]

Slip rolls are not that difficult to use. Start by making sure the third roll is parallel with the pinch rolls. Pinch a sheet between the pinch rolls making sure they have equal pressure and snug it enough to get enough traction to feed the metal through. Try rolling a piece back and forth raising the third roller after each pass. Check your radius with a template or remove the work and hold it on your full size drawing or what have you. Make sure you count the same number revolutions on the adjusting screws to keep the rolls parallel or you will start forming a cone. With this style of small rolls, you won't have trouble changing your mistakes because they can't bend very thick sheet in the first place. The grooves are to keep from flattening a bead that was formed for stove pipe. You could also use the grooves to form coils from round stock. You could even modify them to roll small channels and angles but the angles would need some sort of leg in roll to counteract the camber on an angle.
Mostly bending is a black art and experience is the best teacher. I've been rolling metal for 30yrs now and there are some rules to follow, but not every piece of metal comes out the same.