A function is a preprogrammed set of instructions that returns a value to the user. The Sum of the range A1 through A15 is subtracted from the value in cell C9.
Most functions have one or more arguments that define what the function it to act upon.
The parentheses separate the function name from the information to be used in the calculation. If you make a mistake and would like to start over, click on the X and it will clear the input field. Pressing return or clicking on the check mark will enter the function.