Start by finding the mean of the data set.
Find the sum of the data values, and divide the sum by the number of data values.
Find the value of the difference between each data value and the mean. You can do this by subtracting the mean by the data (d-m).
Find the sum of the differences. Divide the sum of the absolute values of the differences by the number of data values.
Hope this helped. Have a great day!