About the A7 chord
To play A dominant 7th, use the first shape above. Place your index finger on the 1st fret of the C string. Leave the G, E, and A strings open. Strum all four strings and check that each one rings cleanly.
Root
A
Quality
Dominant 7th
Notes
A · C# · E · G
How the A7 chord works
A
Root(1)
The home note. It gives the chord its name.
C#
Major third(3)
The major-third interval that establishes the chord's major base.
E
Perfect fifth(5)
Adds strength and stability.
G
Minor seventh(♭7)
Adds the defining minor-seventh color.