1. How to delete pages
If enabled and allowed by ACLs, you can delete pages with the DeletePage action.
Note that deleting means to create an empty/deleted new page revision, it does not remove any existing revisions of the page.
What this means is that you can get back at deleted pages by reverting them to an older/existing revision (first display some older revision using the link from the info action, then use "revert to this revision" from the menu).
The only way to unrevertably and completely delete a page (including backups, history, attachments, etc.) is via the shell on the host system. The page files are found in the "data/pages/<PageName>" directory, and you can simply delete the whole <PageName> directory - no way back in that case.