i know this is a stupid question...

i know they lower your car, but do they do anything else? if i get coilovers do i have to get like shocks and springs or something like that?

 

They are usually a shock with a threaded outside to mount a spring perch to.

Some are just the sleeve you put over your shocks of your choice.

 

Coilovers you can adjust your ride height manually and as for spring you can't adjust it its sit on that height permanently. Coilover isn't stiffer than normal springs. There are 2 type of coilover real one and just sleeved one. Real coilover cost around 1000 + The sleeves one like Ground Control, Skunk2, etc. cost around 300+ The real coilover has shocks already sleeves one like Chris says it just slides on top of the shock. Use coilovers for show. U can make coilovers ride good with aftermarket shocks like Tokico, Koni, etc. Good luck thats my 2¢