When you have a mass of numbers as your data, it is hard to understand those numbers without creating some measures that represent what the data means.
The first step is to calculate the average or mean. This measure gives you some idea of what to expect from an individual piece of data. I will assume you know how to do that.
The second step to understanding your data is to determine its central tendency or how close the data points stay to the average. This where standard deviation comes in. If you were to average 1 and 99 you would get 50. However, you would get the same average for 49 and 51. The standard deviation (also called the root mean square) measures that variability from the mean.
