Revisions in Guides allows you to easily and quickly switch to a point in history where you were happy with the article you had. It's a built in backup for every change to an article you've made.
Viewing the revision history for an article
Find the article in the control panel.
Select the Revision History tab in the top section of the article editor.
You'll now see a list of all of the revisions.
Click on the "View" button once you've seen the revision you want to view.
Restoring an revision of an article
Click on the "Restore" button next to the article you want to restore.
You will now see on the list of revisions the restored revision is now active and highlighted as well as the "Restore" button disabled.
You can now navigate back to the Edit Article tab to see the article is restored.