dowmloaded a couple of stuff off a torrent site but what do seeds, peers etc.. all mean?

Im an occasional user but may use it a little more now that I can access english TV stuff now that I have broadband in Italy..

so should I peer, seed or whatever?

seed – someone with the whole file(s) who is making it available.

peer – someone with or without the whole thing (you can still get chunks of it from them though even if they don't have the lot).

Generally the more of both the better. If a torrent ends up with no seeds left, anyone left trying to get it will be a bit stuffed.

It's usually considered polite to seed for a while after you've finished downloading. Most torrent clients will show you your ratio (of downloaded to uploaded data) – you should aim for 1:1 at least.

how do i seed?

just leave my computer on?

yeah, i would leave it on over night for a good seeding ratio, but if you got off a site like pirate bay or a site you dont have to sign up for i would do it for 2-3 hrs max