Select STDEVS for a sample from the the Statistical category. It can be calculated by finding the mean of the values first and then find the difference between each value and the mean. With samples we use n 1 in the formula because using n would give us a biased estimate that consistently underestimates variability.
But here we explain the formulas.
You might like to read this simpler page on Standard Deviation first. Deviation just means how far from the normal. How to Find Mean Deviation. Finally we divide this sum by n which is the total number of data values.