If you have a sauce (like gravy, soup, spaghetti sauce, etc) that you need to thicken the easiest way to do so is to use corn starch. But most people just dump the corn starch right into the sauce, and this is not the best way to thicken a sauce. Instead, mix the corn starch with a small amount of cold water and mix it completely. Then add this corn starch liquid to your sauce and mix it in. Doing it this way keeps the corn starch from making your sauce lumpy.