If you are talking about a simple sheet calculating the balance on a bill
after a payment that's a simple thing. Have the formula in column c subtract
the amount in column b from the total you owe.
i.e. =(20,000-b1)
=(500-b2)
If you want the total of column b then you put a sum function in the cell
you want the total displayed.
=SUM(b1:b20)
It all depends on what you are needing.
Regards,
Brian