Before you create any kind of map (color map, bump map, specular map...) you have to unwrap your model, meaning that you have to layout your UVs in order to get a good texturing.
Next you go to the Texture Editor, and you can see your model unwraped. You click UV Snapshot, choose your options and you have a map with your UVs there, ready to paint on.
After that you just have to assing it to the desired slot on the shader.