Getting a root of a number is the same as raising that number to the power of 1/root.
Example:
The square root of x is x^(1/2). The square root of A1 is: =A1^(1/2).
You can also use the built-in worksheet function SQRT: =SQRT(A1)
The cube root of x is x^(1/3). The cube root of A1 is: =A1^(1/3).
You can also use the built-in worksheet function POWER: =POWER(A1;1/3)