You need:
Shoe box lid or cereal box with front panel cut off 
Marbles 
White paper 
Liquid paint 
Newspaper 

Instructions:

1. Protect your work area with newspaper.
   
   
2. Lay a sheet of white paper in the shoe box lid. To make a lid use an empty cereal box, cut the front panel away. If the paper is too big for your lid, you will have to trim it.
   
   
3. Dip a marble in the paint.
   
   
4. Put the marble in the lid and gently lift the lid and tilt it back and forth and side to side.
   
   
5. The marble will make a cool design of paint across the paper. Do this until you are pleased with the effect.
   
   
6. You can use multiple colors of paint. It is best to allow the first color to dry before beginning with the next.