DORIAN is one of the four minor modes and, when compared with IONIAN, has a minor third (b3) and a flat seventh (b7). This in effect has us placing the half steps between steps two/three and six/seven.
Again, and in the same fashion as we did in the first two videos of this SERIES ON MODAL MASTERY, we will work up to a DORIAN chord/scale practice regimen to work out, work up to and master one position at the time. Ask your teacher to suggest some fun tunes to scream over that use DORIAN as the modal center. I can think of so many such as Herbie Hancock's CANTALOUPE ISLAND, Miles Davis' SO WHAT, Wayne Shorter's WITCH HUNT. In short, experiment with different keys for the use of DORIAN.