Mean, in terms of math, is the total added values of all the data in a set divided by the number of data in the set. Make sense? If not, here' an example...
Let's say this is my data set:
1, 2, 5, 4, 3, 8, 7, 4, 6,10
To find the mean...
Step 1: Add all of them together.
1+2+5+4+3+8+7+4+6+10 is what? 50. Now that you have this number...
Step 2: Divide by the amount there are. Basically, count up all of the numbers. How many are there? There are 10. Finally...
Step 3: Divide. 50/10 is 5, so the mean of this data set would be 5. Get it? I sure hoped this helped :)