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
8^{2 ⁄ 3} = 2^{2} = 4.