Add up all the numbers that you have to get a summation of the entire set of values. For instance, if you have 2, 3, 5 and 6, the sum would be 16.
The next step is to count the number of values that you have. For the example specified in step one, the count would be 4.
Use the formula (average = sum/count) to obtain the average. For the previous example, the average would be (16/4 = 4).