Gm mandolin chord
G minor on mandolin is 0-0-1-3, low string to high (G D A E), and it sounds G D Bb G. It is one of the minor chords on the chart.
The shape
Nut at the top, strings running down the page low to high, G D A E. The numbers under the name are the frets in that order. A filled dot is a finger and a hollow dot is the string you add when your hand allows it. An o above the nut is an open string, and a dashed o is an open string you can leave out.
First finger on the A pair at the first fret, third finger on the E pair at the third, and the G and D pairs ring open, exactly as they do in the G major.
The only note that moved is the one on the A pair, B down to Bb. Drop the third a fret and a major becomes a minor, and that is the entire rule. The G on the bottom and the G on top are two octaves apart, which is what gives this one its width.
Where it turns up
The relative minor of Bb, which makes it the vi chord in that key, and the ii chord in F.
A diagram cannot hear you
Mandolin Trainer listens through your microphone, hears which notes of the chord are sounding, and names the string that should be carrying a note it cannot hear, which is the thing a diagram can never do. The Chord Theory section teaches these shapes and then checks them. Free while it is in beta.
Open the appRuns in your browser. The audio never leaves your device. iOS app coming soon.
Other minor chords
Low shapes for the five minors that turn up most. Every one of them is a major with its third dropped a fret and nothing else touched.