 To open the Insert Function dialog box:
Select Formulas - > Function Wizard (in Function Library Group).
Or
Click the fx button on the left of the Formula Bar.
Or
Select a blank cell and press Shift+F3.

 To open the Function Arguments dialog box of a cell containing a formula:
Select Formulas - > Function Wizard (in Function Library Group).
Or
Click the fx button on the left of the Formula Bar.
Or
Select a cell containing a formula and press Shift+F3.
 To insert a new Formula into a cell using the Function Arguments dialog box:
1. Select a blank cell, and then type the equal (=) symbol.
2. Type the formulas first letter and select its name from the drop down list and then press Tab.
3. Press Ctrl+A.


Or
Type the equal (=) symbol followed by the formulas name and press Ctrl+A to open the Insert Function dialog box.
 To insert a formula by typing it while being guided by the formulas syntax tooltip:
Select a blank cell, and then type the equal (=) symbol followed by the formulas name and press Ctrl+Shift+F3.