Guitar chords in the key of C major:
C Dm Em F G Am Bdim

Chord C notes: (G), C, E, G, C and E.

The note G on the sixth string is not required, but can be played on the 3rd fret if needed. The guitar strings 3(G) and 1(E) are left open.

C major chord's alternative names: CM, Cmaj, Do major, C dur.

Steps: 1-3-5.
1(C), 3(E), 5(G).