shade characters

If you go to Backgrounds- Shapes and go to the last page, there should be two circles, pick the one with the dark centre. You can resize this and position it in the parts of your character you want to shade. There are two parts to shading, shadow and highlighting. With shadows you want to have a look at where shadows fall on the human body, usually going for the inner leg, under arm and under the chin are good places to start. Highlighting goes were ever you want it, there’s not really a definitive rules set for either though. With shading the alpha tool on the object colour and the resize tool on the object transform are your best friends, play around with these to get the best effects.
If you want some ideas about where to shade, look at other peoples work. They may look complicated at first, but most of the time it’s just putting in the time and effort, thats what I find.
Hope this is helpful.