Here you find an 'official' Microsoft presentation on Excel formulas.
Remember that formulas are what make a spreadsheet program really useful. Formulas let the user calculate results from data stored in the spreadsheet. They usually refer to cells and changing data in these cells make formulas change dynamically.
After opening Excel, watch the presentation and repeat the actions which are illustrated inside step by step. For this, feel free to use the Excel workbook provided below.
