As you’ve already seen in this section, functions are the engines that drive your formulas. They do the actual processing, whether the formula calls for simple or complex calculations. When you add a function to a formula, the function needs to know which cells to use in the calculation.
Click the cell in which you want to add the function and then click the Formulas tab.
On the far left side of the Function Library group, click the Insert Function button.
The Insert Function dialog box opens.
Click the category down arrow to display the drop-down list and then select the function category that you want to view.
You can choose from All, Financial, Date & Time, Math & Trig, Statistical, ...