Sample Standard Deviation

I dont understand your question. Are you asking why you divide by (n-1) rather than dividing by n?

If so, the difference between the two estimators is very minor in sufficiently large data sets. However dividing by n gives you a biased estimate of the standard deviation, so using (n-1) is usually preferred since its unbiased. I dont know what level of statistics youve studied up to, but any elementary textbook should show you how to compute the expected value of the estimator which divides by n (which is the maximum likelihood estimate) and if you do the calculation you will find it has a bias and that dividing by (n-1) instead removes it.

Generally, most statisticians will prefer an unbiased estimator, most of the time. Using the sample standard deviation is the normal way of doing things, yes.