I suggest reading a book called No Bull Music Theory For Guitarists. That will give you a good background. When you go back to the GT video tutorials it will make more sense.
Gary
[Epiphone Les Paul Standard Plus Top Pro (2), Fender Player Stratocaster (2), Fender Player Telecaster (2), Squire CV 60's Stratocaster, Hamer Ecotone, Yamaha APX600 (2), Epiphone ES-339, GTX-100 (2), Spark 40 (2), Spark Mini.]