ah man, mines a ide, so i gotta get a new one, can you recommended one
Tig recommended one. Given how bad the HDD market is right now, probably the fairest price you'll find, unfortunately.
and what does tower do, whats it purpose, can i just have some parts sticking out of the tower just in case they don't fit and still work?
It encloses everything, helps keep dust out, and helps direct air flow (a case can actually improve cooling). If the motherboard doesn't fit then you'd need to make a custom motherboard mount and have an open air mounting rack, which'll take time and you'll have to be careful, so I definitely don't recommend it, especially if you have small children running about or pets. Same with the GPU, if it doesn't fit, you'd have to take a saw to your case.
You may be better off waiting, honestly. You're budget is tight to begin with (only $500) and you apparently need a copy of Windows ($100 right there) and a hard drive (which as mentioned are very expensive right now due to a shortage).