You may want to review integer exponents and roots first.

Exponents can also be fractions. Raising a number to the power 1 ⁄ 2, say, is the same thing as taking its square root. Raising a number to the power 2 ⁄ 3 is the same thing as taking its cube root (from the 3 in the denominator) and then squaring it (from the 2 in the numerator). (Remember, the cube root of a number is the number whose cube is the original number; so the cube root of 8 is 2.) So 82 ⁄ 3 = 22 = 4.