Always wear eye protection during science experiments. Never handle sharp objects, open flames, chemicals, or other dangerous objects without adult permission and supervision.
Fill the bowl about halfway with water. (It's a good idea to do this in a sink or another area that can afford to get a little messy!)
Gradually add cornstarch to the water, stirring with the spoon, until the mixture is a little bit thicker than cake batter. You can continue to experiment with the thickness of your oobleck later on in the experiment.
Oobleck is a non-Newtonian fluid, which means that it shares properties of both liquids and solids. Try hitting the surface of your oobleck with the palm of your hand. Now, try resting your hand on the surface. What happened?