The letter G at the start marks the treble clef. The real clef is a curly G that wraps the second line up. Piano music for the right hand usually uses this clef. On Glow Keys, that line is G4.
Lines, from the bottom
E, G, B, D, F. A silly sentence sticks: Every Good Bird Does Fly.
Spaces, from the bottom
F, A, C, E. They spell FACE.
Middle C sits on a short extra line just under the staff. On this keyboard it is C4, the white key marked with the computer letter A. Press the note buttons to hear where each one sits.