Then you will get a window that shows all the different versions, their modified date, modifier, size and comments.
Highlight the version you want to compare and then click on the Compare button. Word will open the old version in a new window and then open another window that show both versions and their differences.
On the left you will see a list of the all the changes. In the center is the current document with the changes highlighted. On the right are both versions of the document. Now you have an easy and quick way to see the changes made in each version of the document.