I hear a lot about Jellyfin, may I ask what it exactly is?

Is it like a library of the things, you have downloaded?

I currently just download shows and put them in folders like “MHA S6” and then proceed to watch with VLC.

Anyone know how to get subs to work properly on jellyfin, specifically on a Google TV client? About half of my content has nonnembedded subs with the sub file in its own folder, I can't use subs for those shows, they just don't appear