The role of the tutor is to link something the student already understands to something the student needs to understand. For instance, some people like to drink milk with cookies. These are compliments. There is some amount of cookies and some amount of milk that are required to meet a minimum level of happiness. The amount of each say 8 ounces of milk and 4 cookies is a consumption bundle on a graph, (8,4) a collection of these points defines a curve, ( it could be a line because a line is a curve with a constant slope) and the curve is a utility curve (or happiness curve). The equation that defines that curve is the utility function.