To compare 2 workbooks, opened in Excel, you should use this command on the Spreadsheet Tools tab:

One workbook is considered as older version of the document, and another one - new version. You should select which workbook is old version and which is new in this dialog:

This command compares only sheets with same names in both workbooks. If you need to compare sheets "Balanse Sheet 2008" with "Balanse Sheet 2009", you should use Compare Sheets command.

If your workbook has database structure, please read topic Compare Database Values to find more information about Comparing Database Values options.

When workbooks are selected press Compare button. Now xlCompare has enough data to compare workbooks.

When the comparison has been completed, you get the comparison report, like this:

On this comparison report you can browse list of changes, copy, delete and merge values. All of these features are described in the Working with comparison results topic.