What is a 'rollback'?
I don't understand meaning of first roll back badges. When I move cursor on CleanUp badge it
shows message "First Rollback". What the meaning of this? is we done some action and again
Rolling back a post means that you return it to a previous version.
If there were some edits made to add information to a post that after some clarification are not needed, instead of editing the post again to remove the added information, one could simply "roll back" the post to a previous version.
When you are viewing the edit history of a post (which you can see by clicking on the "edited" link below the post), you can see the "rollback" link as shown in the screenshot below.
That is pretty much the explanation of what a rollback is. With regard to how to earn the "clean up" badge, you can see the possible duplicate link at the top of your post or inspect @alphamale's answer.
Rollback is happened when somebody or you edits your post and you discard that change and roll it back to its previous state. It also remove any offensive flags that have been set on a question.
A rollback involves using a command that is called "Rollback". It shows up when a post that you have edited has the most recent revision by another user. Rolling back will return the post to the last revision that you had made to the post. It requires edit permissions on other people's posts, but is always available on your own posts. For example, I have just edited your post. You should now have an option to "rollback" in the same area that you can flag or edit.
It can also be achieved on a post by rolling back to any revision, by accessing the revision history of a post that has multiple revisions (when you have edit privileges). The option "rollback" can be used to revert to any specific revision, and this qualifies for the badge as well. You can see this here on one of your own questions.
Once a post has been edited, it could be rolled back by anyone with edit permissions for that post to a previous revision. The rollback button appears on the edit page after an initial edit has been made. Note this excludes edits that do not cause a revision history (edits by the OP made very shortly after posting).
You can refer to this question:
Hope this helps.
For rollback first click on the edited as i circled it in image
Then click on rollback