Question

find the standard deviation of 101, 102, 100, 100, 109, 110, 109, 108, 109

Answer 1

Count the number of values in your list, total the numbers in your list. Divide your total by your count and you will have your arithmetic mean.
Subtract your mean from each of your values and square the result, add up your "squared" values and divide by your count OR count-1, population OR sample, to get your variance, the standard deviation is the square root of your variance.