How about this as an exceedingly simple (but hopefully practical) explanation:
Basic Service: I know you are there. I may let you know if I know if there's something that might affect you but don't count on it. Let me know if your engine quits or, preferably, when you leave the frequency.
Traffic Service: I can see you and I'll try to let you know if I think you might have a traffic conflict with someone else. (I think this is the most useful service and personally ask for this as a matter of course).
Deconfliction Service: Traffic service but with vectors to move you out of the way of conflicting traffic.
Procedural Service: Not particularly relevant for VFR flying.