Make 2 solutions:

 

Solution A: An equal mixture of water and Elmer's white glue (add food coloring to make it any color you desire)

 

Solution B: Dissolve as much Borax powder as you can into some warm water (this will probably be 2-3 tablespoons per cup). Don't worry if there un-dissolved powder at the bottom of the container when you are done mixing - just don't use the stuff at the very bottom.

Now mix together equal volumes of A and B & you will get slime. Knead it a bit and let it dry a few minutes and you will have something that behaves a lot like Silly Putty.