Re: making a user Admin
See http://doc.tikiwiki.org/tiki-index.php?page=groups+admin for instructions on group administration. Permissions in Tiki are assigned to groups, not to individual users. If you want every Registered user to be able to create and edit wiki pages, then simply assign the permission tiki_p_edit to the Registered group on your tiki-admingroups.php page. This is a global permission. That is, it applies to all wiki pages.
If you want a page to be an exception to the general rule, then you set that page's permission specifically, clicking its "perms" link and indicating the group that you want the permission to apply to.
For example, if you make a "Site Team" group and want to reserve some pages for them only to edit, then when making the group you include the Registered users group so Site Team will inherit the Registered group's permissions. Then on a Site Team-editable-only page, you give Site Team the tiki_p_edit permission. This will cause other groups (like Registered) to not be able to edit that page.
-- Gary