Most functions in Excel need arguments, or inputs. In particular, all database functions need arguments. You include these arguments inside parentheses. If a function needs more than one argument, you can separate arguments by using commas.
For illustration purposes, here are a couple of example formulas that use simple functions. These aren't database functions, by the way. Read through these examples to become proficient with the everyday functions. (Or just breeze through these as a refresher.)
You use the SUM function to sum, or add up, the values that you include as the function arguments. In the following example, these arguments are 2, 2, the value in cell A1, and the values stored in the worksheet range B3:G5.
=SUM(2,2,A1,B3:G5)
Here's another example. The following AVERAGE function calculates the average, or arithmetic mean, of the values stored in the worksheet range B2:B100.
=AVERAGE(B2:B100)
Simply, that's what functions do. They take your inputs and perform some calculation, such as a simple sum or a slightly more complicated average.