You may want to review powers first.

The *n*^{th} root of a number *x* is the number
whose *n*^{th} power is *x*. For example, the
fourth root of 16 is 2, since 2^{4} = 16. The second root
is also called the *square* root, and the third root is
also called the *cube* root. We write
the *n*^{th} root of *x* like
so: ^{n}√*x*. If we want a square root, then
we don't have to write the 2; we just write √*x*.

Note that a number might have more than one root, or none at all. For example, −4 has no square roots, while 4 has two of them: 2 and −2. When we write √4, though, we will always mean the positive root, 2.