This is the key to understanding how to use music theory effectively and you should NOT SKIP THIS!!!
2nd Part: Scales
Scales are the bedrock to key signatures and chords, as well as tons of solos of course. However they are a combination of intervals and thus have their own character to them, which you'll see in the vid.
3rd Part: Chords
What are chords? Just a combination of intervals, and there are tons of possible combinations (many of which you already know)
4th Part: Harmony
Harmony = combination of chords to make progressions, riffs, and stuff
5th Part: Melody
And this is what it all leads up to. Melody is the skillful interplay of all the elements we've been talking about so far, and there's even more you probably don't know about this concept either......
6th Part: Rhythm
Harmony is extremely important, but you still need a time signature and an idea of what combination of rhythm values you may want......
Last Part: Technique
Finally, this is where you put your harmonics, legato, picking, and other stuff on top of riffs and melodies.
I sincerely believe this is the absolute easiest anyway can make theory without dumbing it down.
Go through everything again if you're having trouble understanding, and keep applying what you learn.