Simple Sums?

Heya, I'm a real noice with excel, so please bare with me!

I use this program to work out my desks' commission at work every day. We have two desks, 930 and 941. The commissions they make go into the same spreadsheet, I currently bodge adding them up but was wondering if there was a sleek way of getting excel to create a total for the 930 commissions, and total for the 941 commissions? the desk number is a cell away from the commission for a trade, if that makes any sense or helps anyone? If this is impossible to understand please forgive me, I really don't sepak excel lol! If anyone could help, I'd really appreciate it

Thanks

Milly