Open Question: How do I create an Excel Spreadsheet to calculate loan payments without interest?

I need help creating a spreadsheet that just subtracts one column from another. Easy stuff except I have no idea what I am doing! I can find formulas for loan payments but they all caculate interest and I don`t need that.

Ex:

Total Payment New Total
$100 $25 $75
$75 $10 $65
$65 $30 $35

Etc, etc.....

Thanks for any help!
Thanks for your answer!
Now...can I format the entire C column with one formula? And if I have the formula A1 - B1 = C1 can I have C1 entered automatically into A2?