Stenciling

In a few words, 

• First cut out a form from a paper (so, there will be a hole), 
• Then put the paper onto the surface that you would like to decorate. 
• Color the blank space in the paper, using a special spray, (that's the best) or a brush. 
• Then take the paper away, and enjoy your finished work.

A tip: try to color with two or more color, not only with one.

Is it difficult? I don't think so...