W=Whole-step=2 frets
H=Half step=1fret
W W H W W W H = Major scale
You get get a crash course on it at my lesson site: http://lessons.mikedodge.com, you'll see the link for the Interval Series.
http://lessons.mikedodge.com
http://www.mikedodge.com
http://www.mikedodge.com