The function p(x) = x^3 is a polynomial. Here the “variable”, x, is being raised to some constant power. The function f(x)=3^x is an exponential function (the variable is the exponent).
Exponential functions tend to get very big very quickly, and though they start out smaller than polynomial functions, they will always eventually become bigger. Notice that the two functions meet at x = 2 and x = 4.