About the C#7 chord
To play C# dominant 7th, use the first shape above. Use your index finger to barre the 1st fret across the G, C, and E strings. Place your middle finger on the 2nd fret of the A string. Strum all four strings and check that each one rings cleanly.
Root
C#
Quality
Dominant 7th
Notes
C# · E# · G# · B
How the C#7 chord works
C#
Root(1)
The home note. It gives the chord its name.
E#
Major third(3)
The major-third interval that establishes the chord's major base.
G#
Perfect fifth(5)
Adds strength and stability.
B
Minor seventh(♭7)
Adds the defining minor-seventh color.