The standard grips this chord is usually shown with.
Abm is Ab, Cb and Eb, a minor triad. The shape this page opens on is written 4211x4, lowest string first.

Also written Abmin, Ab- or Ab minor. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 8 common shapes for Abm on the guitar, and 45 derived voicings in the triad family.
In which keys. Every note of Abm belongs to C# minor (the v), Eb minor (the iv), E major (the iii), F# major (the ii), Ab minor (the i) and B major (the vi).
The common shapes, written lowest string first: 4211x4, 466444, xx6444, xx6897, xx9897, x-11-9-8-9-x, x-11-13-13-12-11, x-14-13-13-12-x.
Triad. Three notes across one string set. Abm has x211xx, xx110x, x2110x, xx644x, xxx444, x664xx, xx6444, 4664xx.
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.