A viewfinder is a piece of paper with a window cut out of it, that is the same shape as the paper you are going to draw on. When you look through a viewfinder with one eye, you only see through the hole. The rest of the world is cut off from your view. This way the artist can create a composition by moving the image within the viewfinder. If you don't like what you see, move it around until it looks right. Then draw what you see on your paper. Viewfinders help to block out information you don't need.
