in order to effectively learn theory like this, you need to:
know all your major scales. to the point that you don't have to think about them
be able to think of your major scales in terms of scale degrees; i.e. replacing the note names with numbers (for example, in the C Major scale, C is I, D is II, E is III, F is IV, G is V, A is VI, B is VII)
know the various intervals (e.g. C up to G is a Perfect Fifth; C to E is a Major Third)
once you do that, you're ready to start learning some heavier stuff