Seeding is a good way to be a good pirate. Some sites show your seed to leech ratio. As a rule of thumb, I usually try to seed double what I leech, but if I find something niche without a lot of seeders I try to maintain until the seeder rate becomes healthy. Simply put, you just don't delete or stop the torrent after its completely downloaded and don't quit your client. Just let it keep going.

You may find that your internet speed drops when seeding. In that case, most clients have a way to cap your upload speeds. Most modern internet speeds can keep up though; it used to be required way back when dial-up and DSL was more prevalent. You know, the good old times of spending three days downloading a movie to find out that it was scat porn.

The torrent protocol works by having uploader (seeders) users sharing their files to downloader users (leechers). Users are topically both seeders and leechers.

With that in mind, to seed a file means to share it with others. And yes, you need your torrent client open for that. QBitTorrent is amazing and doesn't have much overhead in your system, plus you can limit your upload speed and net upload. Some console-based torrent apps are even lighter. No VPS required unless you have specific constraints.