I'm not an expert on making scribbles, but I'm going to teach you how to make a decent scribble really fast using only Paint.

Open up Paint and get your pencil tool (

) and draw a quick outline of your scribble. I'm going to draw a muffin.

Now just quickly outline your scribble. Neatness and perfection doesn't really matter when making scribbles as long as you don't get too sloppy.

Now get a shade a little lighter and fill (

) it in, and draw any important details such as eyes and a mouth.

Now just add any minor details, fill in some darker or lighter areas to give it a better look and you're done.