The standard grips this chord is usually shown with.
Cm is C, Eb and G, a minor triad. The shape this page opens on is written x31013, lowest string first.

Also written Cmin, C- or C minor. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 9 common shapes for Cm on the guitar, and 47 derived voicings in the triad family.
In which keys. Every note of Cm belongs to C minor (the i), Eb major (the vi), F minor (the v), G minor (the iv), Ab major (the iii) and Bb major (the ii).
The common shapes, written lowest string first: x31013, x35543, x6554x, 8655x8, 8-10-10-8-8-8, x-x-10-8-8-8, x-x-10-12-13-11, x-x-13-12-13-11, x-15-13-12-13-x.
Triad. Three notes across one string set. Cm has x310xx, xx101x, 331xxx, x3101x, xx1013, 3310xx, xxx543, x3554x.
The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.