Welcome aboard
wizzard!
Highlighting and shading is quickly and easily accomplished by adding a layer above the image of your choice; filling it with 50% grey and setting its blending mode to overlay. Now take a soft brush and paint directly onto the filled layer (which now appears to be transparent) with white (for highlights) and black (for shadows). Experiment with the opacity of your brushes and, of course, your brush sizes. Use your eraser as necessary.
Hope this helps. Simple and 'effective' and, more importantly, "non-destructive" to your source image.
You might also want to experiment with the "lighting effects" on this 50% grey filled layer!