Watch the Dorian & Aeolian Modes online guitar lesson by Jennifer Batten from Rock Sauce For Lead Guitar
Without getting too deep into theory, dorian and aeolian modes are the two minor sounding scales you should know. If you play an A dorian mode, you are actually in the key of G major, so think of the key root note as one whole step (2 frets) below the A root. If you play A aeolian, you are in the key of C major. The key root note is a minor third (3 frets) above your A root.