To compare 2 selected worksheets, use Compare Sheets on the Spreadsheet Tools tab:

One worksheet is considered as older version of the document, and another one - new version. In this dialog you should select which worksheet is old version and which is new:

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

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

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.