[purple-dragon]

I'd recommend the Hook Theory "books" (there are two volumes). I put the word book in quotes because they are available as both interactive ebooks, i.e., Kindle & iBook, and mobile applications, i.e., iOS & Android.

The authors do a nice job of introducing basic (and then advanced) music theory concepts with text and audio/video examples using recognizable pop songs. They also have some tools for exploring themes further on their website.

I've read the books a couple times and it has given me the ability to reason about existing songs as well as better compose and improvise with songs myself.