Create a new document.

Make sure that it is an RGB image - under the IMAGE menu, then within the MODE submenu, make sure that RGB has a checkmark beside it.

(usually you make this choice when you first create a new document.)

Now press Ctrl+Shift+N - that's the 'quick-key' combo for creating a new layer.

You can also just click your mouse on the small paper icon located at the bottom of the layers palette; on the right hand side.

See if that works.