need help with bike chain

Princeton NJ

Description

first my bike seemed to be skipping on the chain in certain gears. i hooked it up to trainer resistance, and i think that really punked out the chain. now chain will not stay on. i dont know too much about bikes hence the simple explanation and could be a simple fix. although ive asked bike shops to fix the skipping in the past and just gave up on trying to fix that as its only in a couple gears.