Hi William. I am an Excel user like you.
There is a problem with your SUM formula. Right now, that formula reads:
=SUM(F3-G3,"#VALUE!")
The first issue is the cell range to be added by the SUM function. If you are intending to add F3 through G3 you need to express it as F3:G3. The second issue is that you have the #VALUE! listed as a value to be added to the other total. Excel cannot add a text to a number and therefore the formula will always result in a value error.
Your sum formula should be:
=SUM(F3:G3)
If you take care of that issue, you may take care of all of the value errors. If not, then you can use the IFERROR function as Daniell said like this:
=IFERROR(SUM(F3:G3),"")
If you want something entered in the cell instead of a blank cell you can insert it inside the quotation marks at the end of the formula.