Music Theory?

Where do I start? Which lessons? 

This tutorial covers the essential elements of music theory.

https://www.guitartricks.com/tutorial/495/

This collection of tutorials covers those elements in more detail.  It also includes the tutorial above.

https://www.guitartricks.com/collection/music-theory

There are other tutorials on specialized topics that have theory baked into the material.  And each course (rock, blues, country) contains elements baked into the course, applying the ideas in musical skills that are particular to each genre.

It's also important to keep your playing ability & theory knowledge on par & growing together.

Please ask more questions if that doesn't cover exactly what you are looking for.  Hope that helps!

Thankyou!