A shape layer is a fill layer linked to a vector mask. You can easily change the fill to a different color, a gradient, or a pattern by editing the shape's fill layer. You can also edit the shape's vector mask to modify the shape outline, and apply a style to the layer.

To fill a shape with a pattern or gradient:
Select a shape layer in the Layers palette.
Do one of the following: Choose Layer > Change Layer Content > Gradient, and set gradient options.
Choose Layer > Change Layer Content > Pattern, and set pattern options.