Another common type of chord is the dominant seventh chord. It is usually referred to as a "seventh" chord. The chord symbol for the seventh chord is the number 7 written after the alphabetical letter. The symbol for the D seventh chord is D7.
D7
To play the D7 chord, use the first three fingers of your left hand as shown in the diagram, but strum only five strings. Do not strum the 6th string (as indicated by the dashed line).
This is a half note strum.
It lasts for two beats.
There are two half note strums in one bar of * time.
In the following example there are five bars of the D7 chord. Play the D7 chord with two half note strums in each bar. The bold numbers under the staff tell you to strum the chord, the smaller numbers indicate to hold the duration until the next strum.
Now try using both the C and D7 chords. This is a chord progression.