When you need to get sum of a list of vaules depending on one condition, sumif function is here to help.
Lets assume that you have an unsorted list that contains customers and monthly sales revenues which looks like:
You need to get total sales revenue for customer1. Instead of finding sales rev. values one by one for customer1 and sum them, you can use sumif function to do the job. Type following formula in the cell you want your total to shown:
=SUMIF(B3:B13;customer1;D3:D13) (which will result $ 51,650.00 )
This means: sumif(criteria range; criteria ; sum range). İn other words, it checks criteria range (which is customers column), if finds any matches with criteria (which is customer1) ads corresponding sales revenue to sum.
If you are uncertain about how to do it or just lazy, you can also use formula editor: