So when we look at any chord, for instance: Abm - the first thing we want to do is find an Ab note. The same would apply for a any chord: Bm (B), C# (C#), Ebm (Eb), D#m (D#), Cmaj7 (C), Ebm7 (Eb) etc. Always identify what the root of the chord is, first.
Let's examine a quick and easy way to locate said notes on the E and A strings.
To prepare for our bar chord-form to come, let's try adding some notes to these roots. a fifth and an octave. This now makes any root note we're playing into a "5" chord, or a "power chord"