Gradients?

I see people using them for tutorials but I have no idea how to get to it or do that when working. I have PSP9 and am just very curious as to where the Gradients stuff is for layers or adding it. In icons it gives it such a great look! To be able to know how to use it would be wonderful. I also would like to know how do you fill a layer? There are so many layers that I have no idea which one I would be able to fill. I don't know if the proper layer is the raster layer, the vector layer, or the art media layer. It would be great if someone could explain it to me. Thanks ahead of time.