The variance describes the heterogeneity of a distribution and is calculated from a formula that involves every score in the distribution. It is symbolized by s with no superscript. Make the calculations on a piece of paper. You should get a variance of 10 and a standard deviation equal to the square root of 10 which is 3.16. Here's an online demonstration of how the standard deviaiton is calculated, from John Behrens's stats course.
Modality refers to the number of modes a distribution has.
Truly bimodal distributions are seldom encountered. A Bimodal Distribution Hypothetical Data Skewness refers to the asymmetry of a histogram. The histogram above describes the 97 elementary school districts in Arizona in terms of the proportion of poor people in the school district boundaries. Forget about it. There is a relationship among the mean, the median and skewness that is important in descriptive statistics.