1. Standard deviation (s) measures the dispersion of a dataset relative to its mean. The bell curve (also called normal distribution) in statistics is a tool to understand standard deviation. 

Here, 

∑ represents the summation

x represents value of one observation

x̄ represents mean

n represents the number of values 

s represents standard deviation.

Meanwhile, Variance (s2) is a measure of how spread out a data set is. A variance is used to measure how far the data values are dispersed from the mean.

Here, 

∑ represents the summation

x represents value of one observation

x̄ represents mean of all data

n represents the number of values 

s2 represents variance.

NOTE : Standard Deviation is the square root of Variance.