DSST Statistics, standard deviation

[themaboys]

Hi guys,

My name is Tim and I am studying for DSST Principles of Statistics.
I cannot figure out why some places list the formula for standard deviation as "the square root of the sum of (x-mean)^2 divided by (n-1)" and other sites say the formula is "the square root of the sum of (x-mean)^2 divided by (n)"

What does the (n-1) or just plain (n) do in the equation?

Thanks,
Tim