How dose the graph change from point a and point b

“Suppose the graph below is the complete graph of a function f. The Fundamental Graphing Principle for Functions says that for a point (a, b) to be on the graph, f(a) = b. ... The answer is that we don't need a formula for f(x), we just need the values of f(x). The values of f(x) are the y values on the graph of y = f(x).”