Another common type of chord is the dominant seventh chord, usually called a seventh chord. A seventh chord is indicated by the number 7 written after the chord name, e.g., G seventh is written as G7. The following G7 chord contains a new note - the B to the C below Middle C.
The G7 chord contains the notes G, B and F. Play the B with the fifth finger of your left hand, and use your first and second fingers to play the G and F notes, as shown in the chord diagram.