mhhh well I am a beginner too, but someone told me that I can open a new layer and reduce the opacity in it.
and to avoid going out of the borders I should activate the "clipping group" option in a blank layer, this one will only work if the lower layer is visible, that was you will be unable to draw out of the borders of the image below. and there are a option for shades in "mode" just above of the opacity.

I had some problems when I tried to make multiple effects in the same image, so I first fuse these two layers together and then I make a new one.
that is what I know so far, but there is still a lot to learn, like how make light effects.

Owh well, thank you for helping me ... i'll try it later ...

Actually, I'm making a shadow with old color then the basic color. But, my friend said "Your shading is true but have a little wrong". So I must learn again how to shading in here.

Well, thank you again