Variance is the measure of, the spread between numbers, in a given data set. In other words, it means, how far each number in the data set is, from the mean of this data set.

2. Covariance is the measure of, the directional relationship between, two random variables. In other words, covariance measures, how much, two random variables vary together. The word, Directional, means positive or negative variability. A positive covariance, means that, the two variables will change in the same direction, relative to each other. A negative covariance means that, the two variables will change in the opposite direction, relative to each other.

To understand how to calculate a variance and covariance and python code for that you can check this video tutorial.

How to calculate variance and covariance of pandas data columns in python