Coordinate values (x, y) are used to provide a graphical representation of the shape of each function. The ones you listed (radical, rational, linear and quadratic) are types of parent functions that all other similar functions are based upon.
For example, all linear functions are just transformations (generic math term for change) of the original linear function f(x)=x. If you were to graph this, you would start with a set of input values (usually the variable 'x'), and f(x) would become the set of output values. On a coordinate plane, you can graph each of those points to give you a sense of the shape of the graph.
Does that help answer your question?