The Dorian Mode is the 2nd mode of the Major Diatonic Scale ... or in other words, start on the 2nd note of the Major Scale and you get Dorian.  It is a minor scale (b3) with a b7.  It is an incredibly common scale though many folks don't know much about it.  It's used to create melodies over the ii chord in conventional major key music and the iv chord in the relative minor key.  There are also Dorian modal harmonizations where it is the tonic scale.  As usual, there are 12 fingerings for it in our normal chromatic "box" orientation.  Do you need to know all 12?  Not unless you want to be the next Modern Jazz "phenom".  Try to learn as many as you can ... 4 to 6 is a good figure to shoot for.  Start with the easiest ones first ... the ones that have the fewest FINGER SHIFTS (boxes 3 and 10 have no shifts- box 5 has one).  To totally understand your fretboard and how to do finger shifts, visit www.guitar-instruction-free-lessons-online.com/chromatic-scale .  Remember, the RED DOT is your ROOT NOTE and these boxes can be moved anywhere on the fretboard to play in all 12 keys.  If you're unsure how to use these charts, visit www.guitar-instruction-free-lessons-online.com/guitar-scales .  To learn more about the THEORY implications of this and other scales, check out our DVD home study course at www.absolutelyunderstandguitar.com .