Oh man, a ton out there in almost any media platform you like. You could disappear into YouTube for days at a time!
I'm just a hobbyist so learning the nuts and bolts isn't as important as getting a 'good enough for me' mixes. Having said that, learning about compression is huge and a must. I really found this book to be excellent, most would agree. https://www.soundonsound.com/reviews/mi ... all-studio
Like I said, there's TONS out there, just thought I'd start at the ground floor and share what helped me the most.