The larger an error ("actual - predicted") is, the larger it becomes with MSE, since you're squaring those errors.
MAD prevents this from occurring, since we're taking the absolute value of the error ("actual - predicted") to remove negative values instead of squaring the error (like with MSE).
n is the number of periods with a predicted and actual value. yt is the actual value for a given period "t". y-hatt is the predicted value for a given period "t".