Deleting a topic is fairly simple: replace all the WikiText on the page with the single word "delete" (no quotation marks). There cannot be any additional white space (spaces, tabs, carriage returns, etc.).

Before you delete a topic, you should use the "Find References" choice to see if other topics refer to this one. You should also consider whether or not the information has some value.

If in doubt, don't delete.

Undelete

To get back any page that has been deleted, navigate to the page (it will look like a new page at this point) and just save the page. You will then see the version history pane (which includes versions before the page was "deleted"). Restore the one you want and breathe a sigh of relief.