the piano roll is vital. fruity doesn't have too many good plugins for bass or instruments...personally i use Edirol Hyper Canvas as a VST and FM7 as well those are good. the best way to fuck around with it is download like a guitar string at C5, put it into a sampler channel in Fruity, open up the piano roll and just go from there.
sorry if im not too informative. its 6 am , just got back from the clubs, u know how it goes. but if u got any more specific questions regarding fruity i can definitely help u out.