The standard grips this chord is usually shown with.
GmMaj7 is G, Bb, D and F#, a minor major seventh. The shape this page opens on is written 310032, lowest string first.
Note by note. G is the root, Bb is the minor third, D is the fifth and F# is the major seventh.

Also written GmM7, Gm(maj7), G-Δ7 or GminMaj7. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 7 common shapes for GmMaj7 on the guitar, and 30 derived voicings in 4 families.
One note away. Change a single note of GmMaj7 and you have Gm (with one note taken away), Gmaj7 (with one note moved), Gm6 (with one note moved), Gm7 (with one note moved), GmMaj7b5 (with one note moved) or GmMaj9 (with one note added).
The common shapes, written lowest string first: 310032, xx5332, 354333, xx5776, x-10-8-7-7-x, x-10-12-11-11-10, x-13-12-12-15-14.
Under the hand. 1 of the 7 shapes here sits in open position, and the first uses 2 open strings. 1 of the 7 needs a barre. Together they cover the neck from the 1st fret to the 15th.
Shell. Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top. GmMaj7 has 314xxx, 3x43xx, x-10-8-11-x-x, x-10-x-11-11-x.
Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. GmMaj7 has 2100xx, xx4333, 3543xx, xx5776, x9878x, x-10-12-11-11-x, 14-13-12-12-x-x, x1403x.
Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. GmMaj7 has x1x032, x5x373, 3x433x, 6x577x, x9x786, 10-x-8-11-8-x, x-10-x-11-11-10, 14-x-12-12-11-x.
Open string. An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful. GmMaj7 has 3x4330, 6x5770, xx0076, 6x007x.
Tensions. A shell of GmMaj7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (A), the 11 (C) and the 13 (E).
What kind of chord this is. GmMaj7 is a minor chord — root, minor third, fifth. minor chords on every root, and what they are for.
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.