About guitar scales. How to learn and use the pentatonic scale to play melodies, riffs, lead guitar solos, bass lines and songs. How to map the fretboard and connect pentatonic scale patterns. Plus music theory and how to play over chords and progressions.
The song "Hey Joe" by Jimi Hendrix is a series of key changes that end up resolving on an E major chord. The notes of E minor pentatonic share notes in common with all the keys except E. But it still works over the E major chord because it produces a blues sound. For more on these concepts see the threads below.