Assume you have a BibTex post such as the following which you have edited a few times.
By clicking on the "view history of this post" link in the dropdown menu, you see the changes you have made on this post.
By default, particular textual differences are shown between each pair of two consecutive versions.
You may also choose to display the difference between the current version and a specific older version in the history. You can do this by selecting "current version" in the dropdown field of the older version.
If you have chosen to compare a version with the current version, you also have the opportunity to restore particular fields. If you like to do so, first press the restore button which lies beneath the pop-up window. Then, you select the fields you would like to restore, and finally confirm the restore.
By the way: The history of your posts is only visible to you and not to other users, so nobody can see any of your secret mistakes you might have made earlier.
Enjoy the history feature and
Happy Tagging!