In this module, you can study the basic statistical measures of central tendency: mean, median and mode.
The video above from Khan Academy contains an explanation of how to find the mean, median and mode of a set of numbers.
When most people say "average" they are talking about the "mean" of a data set, but in statistics, "average" can refer to the mean, the median and the mode.
Some data sets have no mode, and some have more than one mode!
Use these search terms to find your own resources:
measures of central tendency
measures of central value
how to find mean, median and mode
basic statistics