Next you'll create a new layer and add a gradient effect to it. You can add a layer to a file with the New Layer command, which creates a transparent layer with no artwork on it. If you then add a special effect to the layer, such as a gradient, the effect is applied to any layers stacked below the new layer.
In ImageReady, which does not have a gradient tool, you can apply a Gradient/Pattern layer effect from the Layers palette.