Shading can be quite difficult because you need to be able to picture where your source of light is coming from. So as an example to show you, I drew yellow lines to show the direction the light is travelling.
You add a new layer in between the lines layer and the colour layer. The opacity of the layer should be around 23% depending on how light or dark the colours on your wolf are. Using the lines of light as a guide, you can then shade the areas that would normally be shadowed in real life.
Afterwards, you then take off the guides of light direction
That's the end
Hope it helped
