Drupal has a built in revision system to detect changes in the versions of content. You need to enable it. You can look at the versions in order to return to a previous one.
I made some mistakes here on purpose..
and made some changes in the title and body.
The revison tab shows changes. If you want you can look at the previous versions by clicking the link.
When clicking the button, the Diff module starts to work.. There are three kinds of views.
First you have to check the configuration of the module. Enable the three layouts.
and check the fields you want to use with Diff