Every formula or function must begin with an equal sign. This signals to Excel that the following characters should be interpreted as a calculation rather than plain text.
While you can type numbers directly (e.g., =5+2 ), it is best practice to use cell references (e.g., =A1+B1 ). This allows the result to update automatically if the data in those cells changes. Basic Formulas and Operators Formulas and Functions – Microsoft Excel 2010
When you select a cell containing a calculation, the result is displayed in the cell itself, while the actual formula or function is visible in the Formula Bar above the worksheet. Every formula or function must begin with an equal sign