Shocks/Struts?

I need rear shocks or struts on my 2003 Galant ES 4 cyl. When I push down on my trunk the car bounces for almost 5-6 or seconds and makes squeaky noises. What do I need to replace?

Do I need struts or shocks? What's the difference?
Do I need bellows? And what is it anyway?
Do I need mounts? I think I do...

Any help would be appreciated, thanks.

sounds like rear shocks. id get a set of loaded shocks that come with the spring, shock mounts and shocks already assembled.