- Select the cell in which you want to enter the formula.
- Type an equals sign (=) to tell Excel that you're entering a formula.
- Type the formula's operands and operators.
- Press Enter to confirm the formula.

However, Excel has three different input modes that determine how Excel interprets certain keystrokes and mouse actions:

- When you type the equals sign to begin the formula, Excel goes into Enter mode, which is the mode you use to enter text (such as the formula's operands and operators).
- If you press any keyboard navigation key (such as Page Up, Page Down, or any arrow key), or if you click any other cell in the worksheet, Excel enters Point mode. This is the mode you use to select a cell or range as a formula operand. When you're in Point mode, you can use any of the standard range-selection techniques. Note that Excel returns to Enter mode as soon as you type an operator or any character.
- If you press F2, Excel enters Edit mode, which is the mode you use to make changes to the formula. For example, when you're in Edit mode, you can use the left and right arrow keys to move the cursor to another part of the formula for deleting or inserting characters. You can also enter Edit mode by clicking anywhere within the formula. Press F2 to return to Enter mode.

After you've entered a formula, you might need to return to it to make changes. Excel gives you three ways to enter Edit mode and make changes to a formula in the selected cell:

- Press F2.
- Double-click the cell.
- Use the formula bar to click anywhere inside the formula text.