Monthly total in calculation in Stata

Hi there !
I have time series as year and monthly ( 1975m1 24.2 1975m2 22.2 and so on) ( also as attached). Now i want to calculate the total and average of each months value i e i want to know the average of 1975m1 , 1976m1 1977m1 on and similarly for other months too. Also want o see annual average ie average of 1975, 1976 1977 ans so on. Please suggest ...i am quite new in stata but encouraged to work.
Thank you:)