Find derivative of function, set the deriv equal to zero and solve for x.
f(x) = x^3 - 3x^2 + 13
f'(x) = 3x^2 - 6x
3x^2 - 6x = 0
3x(x-2) = 0
x = 0, 2 <--These are your critical points.
Plug the critical values 0 and 2 into the original equation.
(0, 13) global max
(2,9) global min