How do systems like torrentio + real debrid + stremio work?

I've learnt that there are cached files, that RD already has, but are these files you've already downloaded, or can it be files that anyone has downloaded (I believe it's the latter, but then I'm not sure how that itself works, because isn't that like a big risk, or does each file have some unique identifier and it basically just sees when match??)

What about if you want a file that isn't in the magical cache, do you have to torrent it/find the torrent link and give it to RD yourself? And what kind of speed does it download those files?

And also, will torrentio always use RD (for privacy, like is there a way it might accidentally torrent it instead)? And also, am I able to download the videos (I know you can press download video on desktop, not sure if it's on mobile stremio), and will that use RD, or use the original torrent link and torrent it?

Any help is appreciated, it's my first time using debrid services and I'm not sure I fully understand them (only from what I've seen on this sub, and that it's like a digital lil box you can put torrents in and DDL from them)

Sorry if this is against the rules