hey glitch, it's kinda of hard to explain so i'll try my best:
springs - obviously used to let your car bounce and take the road's bumps and grinds.
shocks - to make sure your car doesn't bounce TOO much w/ just springs. gives the car's suspension a dampening effect.
(real)coilovers - comes w/ shocks AND springs AND the adjustment collar so that you can adjust your ride up and down.
fake coilovers (coilover sleeves) - comes w/ just the spring and adjustment collar. usually people that use this blow out their stock shocks and need to buy aftermarkets, or swap the stock shocks w/ aftermarket ones as soon as they buy the coilover sleeves.
anyone else want to add or change anything i said feel free. hope i helped some.