Counting up from the root, the 3rd and the 5th and adding the 7th note of the major scale (B) gives you a major 7th chord.
This is a beautiful sounding chord, very melancholy and reflective.
Play the "C" major 7 chord and listen to how it sounds.
Song example that use the Major 7 chord.
Jim Croce's "Photographs and Memories" makes heavy use of major seventh chords.
