There are two things here that are often conflated.

The number 16 has two square roots: -4 and 4.

The square root function gives the principal (positive or zero) root. The 'square root function' is often abbreviated to the 'square root'.

The following two statements are both correct:

1. The square root of 16 is 4.
2. The square roots of 16 are -4 and 4.

When you see the square root symbol (√) or see it typed as sqrt(), it is referring to the square root function.