How can I sum credit and debit columns for yearly accounts in Pages formulas?

Tables in Pages are basically mini-spreadsheets.

As such you can use most spreadsheet functions in your table (or even build your table in Numbers.app and copy into Pages).

Without seeing your table, I crafted this example:

The table is formatted with one header row and one footer row.

The main rows of the table are simple static fields (dates and numbers). The footer cells are formulas that just sum the respective columns.

In Footer cell B (credits), the formula is simply:

=SUM(B)

this adds all the values in column B (except the header and footer cells).

Similarly, footer cell D (debit) is simply:

=SUM(C)

and you're done.

There are extra tricks if you have a single column of +/- values, but I don't know what you're aiming for.

If you want a running total, then each cell in column C has to add the cell above, plus the corresponding Credit cell in this row, minus the corresponding debit cell, so:

C2 (the first running total) is simply = B2-A1 (first credit - first debit)

C3 is set to:

=C2 + B3 - A3

In other words, the previous total, plus this row's credit, minus this row's debit.

Fill C3 down the column.

When using a header and footer row, one can also use =SUM(Credit) and =SUM(Debit) in the respective footer cells.