The SAMPLE MEAN is the mean of a sample.
The POPULATION MEAN is the mean of the population.
Different symbols make the distinction between these two, although the formulas are exactly the same.
The ONLY difference between the two is that the SAMPLE MEAN is referred to as "x bar" whereas the POPULATION MEAN is referred to as "mew." BOTH are found by calculating the SUM of all values you are given and dividing by "N," the number of total values.