The mean or average of a set of data represents the characteristic nature or central tendency of those numbers. This is the figure you would expect to occur most often over the long run.
The variance is a measure of how spread out those numbers are among each other. The range between the highest and lowest numbers would indicate variation. Generally, the smaller the range the lower is the calculated variance; the larger the range the higher will be the calculated variance.
The variance is calculated as the average squared difference between each number and the mean. For example, for the numbers 4, 5, and 6 :-