In order to display hidden topics, click on "display hidden topics" below the list of topics. In order to display hidden postings, click on "show hidden replies" below the list of postings.
Afterwards, hidden topics and postings are displayed in grey letters. They can be unhidden by clicking on "unhide" on the right side.
If you do not want to display hidden topics and postings anymore, click on "don't display hidden topics" or "don't show hidden replies".
(1) Unhide topic
(2) Unhide post