The E flat sixth chord is a 4-note chord consisting of the notes Eb, G, Bb and C.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Eb6.
Chords that are a superset of Eb6. The chords include more notes but always Eb, G, Bb and C.
Chords that are a subset of Eb6. These contain less notes but all of them are included in Eb6.
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 Eb6 chord. Feel free to save or share the image as needed.