Umm You know how there are different select modes? The marquee select is the square near the top of the toolbox under the move tool.. Under that is the lasso tool. You basically draw an outline of the area you want to select. 'u' It's really useful. I depend almost entirely on that for my shading.
I don't have it yet, but I'm supposed to get it soon. If you check back with me later once I have it, I'll make you a tutorial on how to use it. I make free tutorials all the time; that's how this one got made. xD; Someone just asked for it. Talk to my friend :iconhoracebulregard: She can tell you how to use the selection tool.
If you can't wait to use it and want to try right now, do this:
-Make a new layer over the color layer -Change the layer opacity to whatever percentage it says to do that step in (i forgot. xD) -Just draw the shading in that reverse flower-looking pattern shown with a small brush and it will look exactly the same. -Merge the new layer onto the color layer and you're good.