Like to sum revenue dependent on the value of two other columns of data.

So I would like a revenue total for all deals by rep x in the month of jan.
The first column would be the month field. The second column would be the
detail of orders by rep. The rep could have one or multiple listings. The 3rd
column would have the revenue associated with that rep for that specific
order.

How do i set it up so the ouput looks for Jan only and rep x only. Then
however many rows that may be, sum the revenue values?