|I'm a little confused about the lay out of your workbook. |
You mention some single cells - O3 and O4 - and then you say you want "Sum" something.
You can COUNT values over a range:
For the table below, this would return 3.
You can use SUMIF to look at one range and SUM another based on what is in the first range.
This will SUM the values in P3:P7, but only in those rows where "them" appears in O3:O7.
e.g. For the table below, it would return 6.
3 me 1
4 them 2
5 them 1
6 me 2
7 them 3