Seeing as the 'intelligent' guys are seemingly not around just yet, this might get you started.
It won't let me post an image, so I'll try to write it.
Keeping Cell D4 blank, In Cell D5 type (without the quote marks) - "=SUM($D$4+B5-C5)" In Cell B5, type your credit amount In Cell C5, type your debit amount
You should see the total appear in Cell D5
Once you get this far, go to the ' Total' cell (D4 in my case), place your cursor on the lower right corner of that cell, moving around slightly until you get a thin + sign. Then 'click and drag' down several cells - this will copy the formula down, automatically changing the relevant cell references.
Unfortunatly, I can't remember how to add to the formula so that you don't get all the '0' showing. I'll work on it but I suspect somebody, much more knowledgeable than I am, will come up with a solution.
So, maybe for now, this will help