In order to restore deleted forums and topic, you must have the Delete and Restore Forums and Topics permission enabled. If the forum you restore contains one or more topics, you will be given the option to also restore the forum's associated topics.
In order to restore deleted threads and posts, you must have the See Deleted Posts permission and Display deleted posts option on the Settings page enabled. If the post you restore is a reply to another post, and the other post was also deleted, both posts are restored.