I'm trying to write a SUM function in sheet B, summing all the data from sheet A in specific rows. I can't find a good explanation of how to do this.
If you want to "retrieve" specific rows, then you need to use the following formula.
=SUMIF(range, criteria, sum_range) =SUMIF(DATA!A:A,"<="&10,DATA!A:A)
In this case, the specific rows are summed , only if the value is smaller or equal to 10.
I've created an example file for you: SUMIF
Try the solution on this page, i.e.: