[excel] If "0" then leave the cell blank

Your question is missing most of the necessary information, so I'm going to make some assumptions:

1. Column H is your total summation
2. You're putting this formula into H16
3. Column G is additions to your summation
4. Column F is deductions from your summation
5. You want to leave the summation cell blank if there isn't a debit or credit entered

The answer would be:

=IF(COUNTBLANK(F16:G16)<>2,H15+G16-F16,"")

COUNTBLANK tells you how many cells are unfilled or set to "".
IF lets you conditionally do one of two things based on whether the first statement is true or false. The second comma separated argument is what to do if it's true, the third comma separated argument is what to do if it's false.
<> means "not equal to".

The equation says that if the number of blank cells in the range F16:G16 (your credit and debit cells) is not 2, which means both aren't blank, then calculate the equation you provided in your question. Otherwise set the cell to blank("").
When you copy this equation to new cells in column H other than H16, it will update the row references so the proper rows for the credit and debit amounts are looked at.

CAVEAT: This equation is useful if you are just adding entries for credits and debits to the end of a list and want the running total to update automatically. You'd fill this equation down to some arbitrary long length well past the end of actual data. You wouldn't see the running total past the end of the credit/debit entries then, it would just be blank until you filled in a new credit/debit entry. If you left a blank row in your credit debit entries though, the reference to the previous total, H15, would report blank, which is treated like a 0 in this case.