To add a new page to Wiki, all you have to do is come up with a meaningful title, capitalize all the words and StringThemTogether. Wiki automagically recognizes it as a hyperlink. Alternatively, you can put anything into [square brackets].
Note that short, capitalized titles are much preferred over verbose titles in square brackets. Instead of [This is a page telling you how to do something], rather write "This is a page telling you how to DoSomething". With time, you will realize why this is much easier to handle.
Then you can go ahead and click on the question mark right beside your page title, and the Wiki will give you a window for creating the new page.
If you wish to add documents with complex markup to the Wiki, you might be better off providing a URL to it than trying to add the text of the document here, like so:
PhpWiki project homepage: 
http://phpwiki.sourceforge.net/
The Wiki does not support HTML tags (see TextFormattingRules). <tags>They will just render like text.</tags> Wiki is meant to be as simple as possible to encourage use.
Note that there is a feature that your system administrator can enable to allow embedded HTML, but there are security risks involved.