Section one
Am - D use the A dorian mode (relative major = G)

Section two
Em - B7 use the E aolian over the E (relative major = G) and then switch to the E harmonic minor over the B7, or the B mixolydian mode

Section three
Runs through three II V I progressions:

Em7 - A7 - DM7 (relative major = D)
Dm7 - G7 - CM7 (relative major = C)
Cm7 - F7 - A#M7 (relative major = Bflat)

This section ends with four bars of Bdim.

This track is ideal for learning, exploring and practicing the dorian mode, the harmonic minor scale, changing keys mid-track, and is also an opportunity to explore playing over diminished chords.