Replying to Sub for toyota

i have absolutely no idea about anything on this, but

i want to put a sub in my '92 toyota 4runner. obviously, it has the piece of shit deck in there, but i don't want to get a whole new flashy one like everyone has, because it would be more than the truck is worth, so can i hook up a sub and have it run to the piece deck that's already in there? or do i have to buy a deck as well as a sub.

and an amp too, do i have to buy one of those?

any help at all would be appreciated.