The mean is the average. Add up all the numbers. Divide the sum by however many numbers there are. To find the median, list the numbers out from least to greatest. Take a number off the left, then a number of the right. Keep going until you have one number left in the middle. This is the median. If you have two numbers left, add them together and divide the sum by 2. The mode is the number that appears the most. If two or more numbers appear the same amount of times, they are all the mode. As for stem and leaf plots, you can Google them. They're really easy.