Try setting up a select query with your criteria then click the Totals button on the ribbon. The view will change slightly. You should be able to figure it out, even if it takes a bit of playing, but that's how you learn. Depending on what field(s) you choose to Group By, you may end up with identical sum values in every record but that's how it works. You may have to removed fields from the Grouping. If you need them later, often the solution is to create a totals query then query that query.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.