Yes, before installing vinyl tile onto concrete you must treat the concrete to make sure that it is free from grease, dirt, paint, and other materials. Your tile work will only be as smooth as the concrete below it. Use a heavy duty all purpose cleaner and utility knife.
Yes. Never install vinyl tiles on raw concrete. First, clean thoroughly, then patch any holes or cracks with a patching compound. Finally, use a self leveling compound according to directions. If you don't prepare the surface, your tiles may curl and not stick, or even crack in two.
Clean the floor well with concrete cleaners, let it dry completely. If the floor needs leveling in areas do so with a leveling agent sold in the hardware store. I used sticky back tiles in our basement bathroom and 4 years later there still there. Looks good as new.