When a post has been edited after it has been created, the post shows the user who edited the question. The timestamp shown after "edited" is a link to the revision page, which shows all the revisions for that post.
It's not considered a new revision if the edit has been done in the 5-minute grace period; this means that if the user creates a post, and then edit it before 5 minutes are passed, the "edited" link will not appear.
In the revision page, you rollback a previous version by clicking on the "rollback" link shown for the revision you want to restore.
The "rollback" link is visible to the users who can edit the post, which means:
- to the user who created the post, independently from the reputation that user has
- to any user with the privilege of editing any post, which is a privilege gained when the user's reputation is at least 2000
When there is a pending suggested edit, you are probably not allowed to rollback a previous revision, without first approving the suggested edit; as I have never been in that situation, I cannot say it's exactly what happens.