C and G finish your set of beginner open chords. With D, they make the three main chords in the key of G major.
C: ring finger on the A string, 3rd fret; middle on the D string, 2nd fret; index on the B string, 1st fret. The open G and high e must ring, so keep your fingers arched. Strum from the A string.
G: middle on the low E, 3rd fret; index on the A string, 2nd fret; ring finger on the high e, 3rd fret. Strum all six strings. (Some players use the pinky on the top string; either is fine.)
Pick each string on its own first. In C, the open G string is the one that usually gets muted by the ring or middle finger. Roll your wrist forward a little to give it room.
Then strum four downstrokes per chord. G-C-G-D should sound open and bright.
The most common mistake is a stretched C shape with a flat index finger, which mutes the high e. Keep your thumb low behind the neck so your fingers can come down from above.
