I've been playing for 2 years now and I always looked at the cinematics as just teasers or promotional videos. I know there's a fair bit of lore in the game but when I watched this and saw comments there's so many things I don't know about. Like wtf is a Legion? Omega? Alpha? Earth-1? What the heck are these terms.

Where can I find sources, preferably videos, but could also be text about the game's lore? Suggest some youtubers, sites, youtube videos, and all that cause I'm genuinely interested.