To see what changes have been made to an article, you need to view its article history.
Go to an article and clickon the side bar.
This is the history of an article about taking screenshots. See how the history shows the edits a person made to the article. You can also see who made the edits, the date on which the edits were made, and what the edit was for. Click on a date to see what the article looked like on that date.
Sometimes when you go to edit an article, you'll see this warning message.
It tells you that there have been newer, unpublished revisions made to this article. Make sure that you're editing based on the latest version of the article.