The sites are purposefully obtuse to not draw attention.
A debrid service generally has 2 purposes: caching files and unlocking premium file hosting sites for cheap.
The latter is self-explanatory and not relevant for this thread (basically imagine unlocking premium for sites like mega and rapidgator but only paying 1 site for all of it).
The former is what’s important. When you give a site like real debrid a torrent/magnet link, it will download the files in that torrent and cache them so that anyone who later wants to access that same torrent, instead of having to rely on seeders, can just download it directly from the debrid website.
What are the torrent sources?
It doesn’t have any, users are the ones who manually (or automatically with their API) provide the site with torrents, which the site then caches for anyone who later wants them.
Also, what about seeding ratios?
There aren’t any. Most debrid sites only leech and don’t seed, that’s why even among piracy communities they can be controversial.
And then another comment points out that streamio is meant to work directly with torrents, which leaves me confused as far as how all the pieces fit together.
Stremio doesn’t do anything on its own, the add-ons built for stremio are what do the work.
There is an add-on called torrentio which can pull torrents from several popular trackers and show them in stremio, where you can pick one and start streaming (or, more specifically, the stremio app downloads the torrent sequentially, which allows you to watch it while it’s still downloading). That’s what we’re using here.
This add-on can additionally be configured with your real debrid account’s API key so that when you select a torrent in stremio, instead of stremio downloading the torrent normally from the available seeders, it instead pulls the cached file from real-debrid, dramatically increasing download speed and more or less eliminating buffering altogether (since real debrid can provide the file at much faster speeds). Using real debrid also solves the issue of torrents with no/few seeds, since the file is always cached regardless and can be provided at fast speeds always.