C/G Piano Chord
C/G is a C Major chord played over a G bass note. Because G is the 5th of C Major, C/G is simply C Major in 2nd inversion, the same notes with the 5th moved to the bottom.
The dark key is the bass note (G); the coloured keys are the C Major chord tones.
Notes in C/G
Low to high: G (bass) , then C – E – G.
How to play C/G
Play the bass note G low in your left hand, and the C Major chord (C – E – G) in your right. Because it's an inversion, the bass is already one of the chord tones: you're just voicing C Major with its 5th on the bottom.