This tutorial is abot how to shade in a basic way (steps 1-3) and to do some more fancy stuff (4-6).
I have used digital tools but it works using traditional colors as well.
Start by using Step 1-3. If you would like to conduct experiments afterwards use steps 4-6. :)

Step 1:
- Apply your opaque basic color.

Step 2:
- Add a lighter spot towards the direction of the main lightsource (I will add an explanation on how light exaktly works later in an other tutorial) I chose the upper right direction.

Step 3:
- If there is a light spot you need a dark area, too. Gently mold the bottom left side darker.

Fancy step 4:
- The environment of an object reflects the lightsource and casts a slighty light edge to the opposite site of the lit area.

Fancy step 5:
- Lightsource may be colored. I changed the lit area to a light yellow (perhaps sunlight?), aswell the lit edge.

Fancy Step 6:
- Make it shiny by adding a nearly opaque white spot in the center of the lit area!