I learned it from my guitar teacher as an adult. Started with scales and ear training, then onto what chords were, modes and then chord substitutions and things

I learned it from my guitar teacher as an adult. Started with scales and ear training, then onto what chords were, modes and then chord substitutions and things like that. Most of the weird stuff I know about music comes from YouTube videos, though, and I'd recommend Adam Neely or Rick Beato because they'll probably have a video in their catalogues that you'll enjoy. Learning the basics will be boring, not going to mince my words on it. Treat it like a pattern exercise, since that's what most of it is. The theory is stupidly dry, as useful as it can be, but I don't think there's really any other way to learn it beyond wrote learning.