excel course in london - Tracking changes

To track changes you need to first share the workbook, and then enable tracking.

On the Tools menu, click Share Workbook, and then click the Editing tab.
Select the Allow changes by more than one user at the same time check box.
Click the Advanced tab.
Under Track changes, click Keep change history for, and in the Days box, type the number of days of change history that you want to keep.

(change history: In a shared workbook, information that is maintained about changes made in past editing sessions. The information includes the name of the person who made each change, when the change was made, and what data was changed.)

Click OK, and if prompted to save the file, click OK.

I recommend reading through the Excel help file to familiarise yourself with how it works. Simply type "track changes" into the help search area of excel.