In sound, nothing beats personal experience, experimentation and hours of deliberate listening. Spend a couple of hours with a basic compressor built-in your DAW and try to get the feel and understanding of how each parameter affects different sounds (from sine wave and noise to voice to drums, etc.). If you feel it's not fruitful, read, watch videos, listen, work on your stuff and come back to it after a while.
Regarding books, there's lots to choose from. For some quick applied wisdom, Bobby Owsinski's Mixing, Recording and Mastering Handbooks (separate) are recommended. Zen & The Art Of Mixing by Mixerman is very good, as well as his classic The Daily Adventures. The Bruce Swedien Recording Method is very good if you're into recording.
For Youtube videos, some random things I can vouch for:
I'd suggest watching Monty's Digital Show and Tell [1] as a primer for digital audio as a form. Steve Albini has been putting out some very solid and entertaining videos on recording lately [2].
There's also of course a few hyped (but deservedly so) channels such as @DanWorrall, @Producelikeapro or @ProductionAdvice.
Nothing I can suggest for courses as I haven't been interested in them for a while.
[1] https://www.youtube.com/watch?v=cIQ9IXSUzuM
[2] https://www.youtube.com/@ElectricalAudioOfficial/videos