You’ve never re-watched a movie?

Full speed? Laughs in 62 books and counting for a single sub-series

Don’t know a lot about the fantasy half but a great way to start with 40k is on youtube with Bricky’s videos on every faction explained. Or if you really wanna dive into the deep end, starting on the first book of the Horus Heresy is a great way to set the scene for things to come.