So if you have the app you will learn hoe to shade if you don't You can still learn

So How I shade is very simple

I take a light or dark color

Light color shading:

I took screen shot of me Drawing my oc Wendy

Than Color it in:

Than you get a darker color like this:

normal color

Darker color

So now You do this:

Than you go to the paint brush and press the FX:

Press FX
Than press:

It will show this

Make it go until it looks like this:

Now dark color shading Follow all the steps on the first one but instead of darker color shading I use light color shading when it comes to dark colors

Hopefully this helped you guys out if it didn't than I least I tried