How do I do the following:

Column B (add)
Column C (minus)
Column D (total of A minus B)

example

Column A Column B Column C Column D

Paid In 20.00 20.00
Debit 10.00 10.00
Debit 5.00 5.00
Paid In 150.00 155.00

I need the running balance in Column D - hope someone can help Im trying to
put my accounts on Excel.

Thanks
Sierra_Louise

ps: i need an IDIOTS GUIDE because Im new to Excel