Hey guys. I want to know what these little 2 note structures are called. I hear them in alot of blues and rock solos?

http://www.youtube.com/watch?v=le4PeKpZKCk

from 0:12 to 0:19.........Then again from 4:00 to 4:05

How do i practice and see them on the fretboard. How do you find the key they can be played in when i hear a peice of music i want to play them over? They have always confused me. What ARE they?

Please help, they frustrate..