The square root of 256 is 16. A square root is the inverse, or opposite, operation of squaring. This means that the means of finding the square root is to determine which number multiplied by itself results in the integer in question.
There is no perfect way to find a square root; most people rely on a calculator. However, if a number is a perfect square, then the square root can be found using estimation. For instance, to determine the square root of 256, an estimation can be made. 12x12=144 which is too low; 20x20=400 which is too high. The number must be somewhere in between 12 and 20. Directly in between 12 and 20 is 16, and 16 x 16 = 256.