Set the paints beside your liquid cornstarch dish and grab the plastic dropper. Use the dropper to grab some paint from the top of the cup. Gently graze it across the starch dropping little drops as you go. If your paint is simply falling to the bottom without dispersing along the top it probably means your cornstarch mixture is too thin and you should boil it down a bit more to thicken it up. Ideally you want the cornstarch to be thicker than the paint. You can also try watering your paint down a little bit more to see if that helps.