I have never really used Excel before but this seems like it should be possible.
I have an ongoing document where I will be adding values every day, but what I want it to do for every 7 rows I want it to sum those values and add the sum of the 7 rows to a different column/row, e.g.,
Row B7:B14 Sum in D12
Row B15:B22 Sum in D13
And then when I start adding data into B23 I want it to add the sum to D14.
In D12, put
=SUM(OFFSET($B$7,(ROW()-12)*8,0,8,1))
and fill down column D as far as you want. Note that B7:B14 is really 8 rows, not 7. If you really want 7 rows (B7:B13), then change the two 8's to 7's in the formula.