A few questions about leeching and seeding?

Seeders are people who are sending the file out at the moment. Leechers are people who are pulling the file down at the moment. How many times a file has been downloaded is a separate statistic. As to seeding a stopped download, that depends on your client. Some wont seed an incomplete file unless they're also downloading the rest, but some allow you to partially download a torrent and seed the parts of it you've downloaded. Generally the ratio is how many bytes you've downloaded vs how many you've uploaded. Two to one is considered polite, but at least do 1.5:1. Thus if you download 1 gig, you should seed until you've uploaded at least 1.5 gigs.