If you don't care to remember the exact function names or the required arguments, you can select the function from a master list in the Functions dialog box. When you select a function from the Functions dialog box, you are immediately taken into the Formula Composer to finish creating the formula. The Formula Composer helps you build the formula by reminding you which elements are needed and alerting you if there is an error.
To select functions and use the Formula Composer to build the formula
Click (or double-click) in the cell where you want to add the function.
Click the Insert a Pre-existing Formula button ...