A formula is an expression telling the computer what mathematical operation to perform upon a specific value. When referring to computer software, formulas are most often used in spreadsheet programs, such as Microsoft Excel. Using formulas in spreadsheets can allow you to quickly make calculations and get totals of multiple cells, rows, or columns in a spreadsheet.
In the picture below is an example of a Microsoft Excel formula =SUM(A$1:A$3), which adds the total of cells A1, A2, and A3. In this formula, SUM is the function of the formula.
Press the shortcut key Shift+F3 to open the Excel Formula or Insert Function window.
A formula is not be seen unless the cell is selected.