nutcracker,
It is just like I said.
The IF() function has 3 arguments: the logical test, the result if true, and the result if false (in that order.......separated by commas).
=IF(Logical Test, Result if True, Result if False)
So, using your example:
Logical Test = [c43=""]
Result if True = [""]
Result if False = [+sum...]
=if(c43="","", +sum...)
the commas just separate the 3 different arguments.
so your equation is saying "If cell c43 is blank (or appears blank), then this cell should appear blank, else this cell should display the results of +sum..."
HTH,
Conan