Composite functions are formed by combining two or more functions together. To evaluate a composite function, you first evaluate the innermost function for each value in the domain and then use those results as the inputs to the outer function. For example, if f(x) = x^2 and g(x) = x + 3, then the composite function g(f(x)) would be evaluated by first applying f(x) = x^2, and then using those results as the inputs to g(x) = x + 3.