Making a wiki page is the easiest thing in the world...
Just type the title you want into the wiki search box, and so long as no-one has created a page with that title already, it tells you the page doesn't exist and asks if you want to create it. Just say "yes", and then paste/type on whatever you want in there!
Most of the code and stuff, like the contents list and titles, all handles itself...
put "=" signs either side of each title. The more signs the further the indent.
= Level one heading =
== Level two heading ==
=== level three heading ===
and so on.
Use the buttons for other formatting, embedding links, pictures etc...
The only strange thing is that there is no Wiki-code for underline, but fret ye not! Unlike Buletin Boards (like this one) Wiki interprets HTML, so just use the HTML tags for underline:
<u>underlined text</u> - always remember the close tag!
Tables, also, need to be created in html, but the table code is far more versatile in HTML than in BBCode, letting you create borders and things.
That's it really...