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

Chord Cm notes: C, D#, G, C and (G). You should not play the 6th string.

The note G on the first string is not required, but can be played on the 3rd fret if needed. The string 3 (G) is left open.

C minor chord's alternative names:
Cmin (Do minor, C moll).

Steps: 1-b3-5.