The mean of a set of data is the arithmetic average. To calculate this value, add all the data together and divided by the number of data. For example, here is a set of data, 8.9, 8.8, 9.0, 8.6, and 8.5. Add everything up and you should get 43.8. Divide this number by five, and you should get 8.76 as the mean.
The median is often confused with the mean, but it is not actually the same thing. Median is the number in the middle of a set. For example, when you have an odd set of data, you should rearrange the data from small to large. Then there is a number in the middle, that number is the median. See picture below; the number that is circled is the median.
For an even number set of data, you should also rearrange the data from small to large. The median is the two numbers in the middle. They can both be called median or some people simply take the average of the two for one value of median. See picture for more information, the two numbers that are circled are used to calculate mean.
The mode for a set of data is the number that appears most frequently. For example, with a set of data that has ten values, the mode is the one value that appears more times than others. For example, the mode is 7 in this piece of data, 1, 2, 3, 4, 5, 5, 6, 7, 7, 7, and 10.