It may help to remember that postings on a wiki can always be edited again later, by you or by others. I find that this takes a lot of the stress out of the editing process, since you know that you can always go back and fix things -- and that others can also fix any obvious errors they might spot, or add their own information to yours.
It may also help to remember that earlier versions are always saved; wiki admins have the magic power of reverting a page to an earlier form with a few mouse-clicks, but even ordinary mortals can retrieve lost bits of text from earlier versions of a page by clicking the "history" tab.
For more technical information about MediaWiki, see the HTYP MediaWiki article.
- Bold and Italic are easiest to do by highlighting the text you want affected and clicking the bold or italic button at the top of the edit window, but they're also easy to type in: ''italic'' '''bold'''
- Internal Links to other pages within the same wiki follow this form: [[Name of Page|text for link]]
- External Links to web pages outside the wiki follow this form: [http://google.com/ Google]
- Headers are indicated by enclosing the header text within equals signs: =Level 1 Header= ... ==Level 2 Header== ... and so on.
- Lists are indicated by beginning the line with any of the following characters: "*" for bullets, "#" for numbered lists, ":" for indentation with no mark or numbering. You can also combine these, e.g. if a line starting with "#" is followed by a line starting with "##", that line is double-indented and begins its own numbering. The next line starting with just "#" resumes the original numbering. (There's a page about this somewhere in the MediaWiki Manual, but at the moment I can't find it.)
- images: how to do images on a wiki