Show me how to create custom formulas in Microsoft Excel 2007

Excel -> Microsoft Excel 2007

Problem: I need for certain cells to be automatically calculated based upon the values that exist in other cells.

Open Microsoft Excel 2007
Select a cell and type "="
Type the coordinates for another cell containing data (e.g., "D9" or "H3" or "B22")
Type an operand (e.g., "+" or "-" or "*" or "/")
Type the coordinates for another cell containing data (e.g., "D9" or "H3" or "B22"), or type a numerical value (e.g., "5" or "12.2" or "-9")
Click the "Enter" key