First understand that when a number is multiplied by itself, you get the square value of the number. When you have a number that you need to get the square root you find a value that mltiplies itself to give the original number.Example
The square root of 36 is 6 because 6*6=36
For the nearest hundred, you check the tens place value digit of the number.
For example , the square root of 25255 will be
The answer will be: 158.92, then to the nearest hundred, you check the tens value, which is 5 in our case, if greater than 5, you add 1 to the value infront to get 200 as the final square root value to the nearest hundred.
So in summary, get the square root of the given value, then check for the tens place value digit in the answer and if greater than 5 ,round it off as show in the example.