For this you will need some things. heres a list.

• Paint.net
  
• shading template
  
• a brain
  
• a skin to edit
  

for paint.net, go to Here. click the Free Download Now: and then open the file. double click the only thing in there. 

now download a shading template. you can find these all over the place, just find one that looks nice too you!

now, open up paint.net and load up your skin and template on seperate layers.now, on the template layer, press F4. go to properties, and ,make it overlay.

thats it! have fun! leave a diamond if this was useful please!