Standard Deviation for population & sample?

If the data given is sample from population, use sample formula. If it's of whole population, have to use population formula. The difference is for sample the denominator is N-1 where as for population it is N. The formula is Square root of [total of squares of (x-average)]/N for population and Square root of [total of squares of (x-average)]/N-1 for sample.

standard deviation use to find out  the how spared out the data from mean value,