To calculate the standard deviation of a set of numbers, you can use the following steps:

- Calculate the mean of the set of numbers.
- Calculate the difference between each number and the mean.
- Square each of these differences.
- Add up all of the squared differences.
- Divide the sum by the number of items in the set.
- Take the square root of the result.

Here is an example:

Suppose you have the following set of numbers: 1, 2, 3, 4, 5

- The mean of this set is (1 + 2 + 3 + 4 + 5) / 5 = 3
- The differences between the mean and each number are -2, -1, 0, 1, 2
- The squared differences are 4, 1, 0, 1, 4
- The sum of the squared differences is 10
- The mean of the squared differences is 10 / 5 = 2
- The square root of 2 is 1.4142135623730951

Therefore, the standard deviation of this set of numbers is 1.4142135623730951.