What is the square root, and how do I calculate it?
The square root of a given number returns a number that, when multiplied by itself, returns the original (given) number.
For example:
The square root of 4 is 2, since 2 * 2 = 4
The square root of 36 is 6, since 6 * 6 = 36

Taking the square root of a number is the same as raising the number to the power of 0.5, for example:
36 ^ 0.5 = 6

To calculate the square root of a number, you can use any calculator that is available to you (look for a √ button). To calculate a square root by hand, you need to start with 2 numbers, square them, and then estimate a new candidate for a square root. To understand this better, I will give an example for determining the square root of 10:
3 ^ 2 = 9
4 ^ 2 = 16
-> the square root must be somewhere between 3 and 4
3.5 ^ 2 = 12.25
3.25 ^ 2 = 10.5625
3.1 ^ 2 = 9.61
-> the square root must be between 3.1 and 3.25
...
this can go on forever, since the square root of 10 is an irrational number, which means that it has an infinite amount of digits after the comma without any pattern. Calculators will display the amount of digits they are able to calculate.