Get average on total (sum)

My first question... and first time to Power BI and DAX (experience Excel user).

I have 5 data sources that gives me monthly usage, for years. So 12 data points per year for each source.
Now I liked to see the average total usage each month, allong with the average usage for each data source.

The output should be something like, with 3 data sources:
Month | S1 | S2 | S3 | Total
Jan | 0,1 | 0,4 | 1,1 |  1,6

Feb | 0,2 | 0,3 | 1,0 | 1,5

etc..
(Where S1/Jan 0,1 is the average usage for January for all years.)

How? I feel I dont know were to start..