The Major Diatonic Scale (also known as the Ionian Mode) is the central scale in Western music.  It's that "Do-Re-Mi" thing they taught us in kindergarten.  It's a myth that Pentatonic Scales are more important to know about. Our whole concept of "keyness" and key signatures is based on it as well as our musical number system.  It is used to create melodies over the I chord in conventional major key music and the III chord in the relative minor key.  It's interval pattern is mostly whole steps except between 3 and 4 ... and 7 and 8.  As with all scale, there are 12 different fingerings within our chromatic "box" orientation.  Do you need to know all 12?  Not unless you're looking to be the next Modern Jazz "phenom".  Try to learn as many as you can ... 4 to 6 is a good figure to start with.  Learn the EASIEST ones first.  They're the ones with 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 about how these charts work, go to 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 program at www.absolutelyunderstandguitar.com .