Averages
There are three main types of averages, the mean, the median and the mode.

The mean  The mean is essentially the average that you are probably used to, where you add up all of the values and then divide that number by the number of values that there are.

The median  The median of a group of numbers is the number that is in the middle of the set when the numbers are in order of magnitude. E.g to calculate the median of 2, 5, 2, 8, 4, 6, 3, you first put the numbers in order  2, 2, 3, 4, 5, 6, 8, then you look what number is in the middle which in this case is 4.

The mode  The mode of a group of numbers is the number that occurs the most. For example in the set 2, 5, 2, 8, 4, 6, 3, 2 occurs the most amount of times which means that 2 is the mode. A good way to remember this is mode is the most.
The range is the largest number of a set take away the smallest number. For example, to calculate the range in the set 2, 5, 2, 8, 4, 6, 3, you would take 2 from 8 (82) which equals 6. Six is the range.