Key

[Topbanana]

On a keyboard how do you know what key a piece of music is in just by looking at it

[Sarahmitz]

If you can't read music i.e the key signature, then play the chords. Maybe, try the guitar chords usually on top of the stave. If it starts with G. start on G and run 7 fingers up the keybaord using both black & white until it sounds correct. The correct key is defined by which white & black notes you use. e.g C has no black notes . D has two. A has three. It's a little more complictaed than that , but why not enjoy and play. If you have an ear, it's irrelevant you'll pick up as you go along. Enjoy music!!!!

[tamborine]

You tell the key by the written notes grouped together on the bass (left hand).