Place a sheet of paper on top of a material that you’re allowed to get messy (like some old newspaper or a piece of cardboard). Dip a paintbrush into some watered-down paint, hold the brush over the paper with one hand and tap it with the other to create splatter and drips on the paper. Do this three times with a different color paint each time. This is called “action painting.” American artist Jackson Pollock painted in this way.
Jackson Pollack. 
When you are done and the paint has dried, cut out a smaller square shape and glue it into an empty page in your My Year of Art sketchbook.