The G flat major chord is a 3-note chord consisting of the notes Gb, Bb and Db.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as GbM.
Chords that are a superset of GbM. The chords include more notes but always Gb, Bb and Db.
Chords that are a subset of GbM. These contain less notes but all of them are included in GbM.
In case you prefer a non-interactive variant of the chord chart, we've embedded a PNG image below that shows the notes for the the GbM chord. Feel free to save or share the image as needed.