This Wiki (the GeoWiki) is run by the Geocaching Australia community to store frequently asked questions, document how to use the GCA website, etc. The main entry point into the Wiki is the Main Page.
The collaborative nature of a Wiki is that if people think that there should be a section on XYZ, they can just write it and it will appear!
Using the Wiki
To read stuff, just click on the links as normal. If you want to edit a page, click the edit tab on the top of the page. You'll see some stuff which looks like phpbb code. Just have a look at what's there and you'll get the hang of it. Enjoy!
Here is the User's Guide.
What is a Wiki
For those of you who have never seen a Wiki before, it's a tool to allow collaborative document creation. Bsically it's like a giant whiteboard where people can write documents with links between them. 
Logins for editing the Wiki
Editing a page
If see something you want to change or add to an existing page, it's very easy once you have a login:
1. Go the article you want change.
2. Click on edit.
3. Make the changes you want.
4. Click on Save (or Preview first if you want to be careful).
Adding a page
Anyone is free (and encouraged) to add content to the Wiki. To do so:
Go to the page you want the article linked from and put in the link. Then click on that link and you will be able to edit the new page:
For example, assume you are in the [Geocaching] page and want to do an article on coordinates:
1. In the [Geocaching] page, click on edit.
2. Change the text "coordinates" into the link "[[Coordinates]]"
3. Press save
4. See how all the links on the page are blue yet the coordinates link is red. that means it's empty.
5. Click on the coordinates link and you'll be able to add text
6. Press save and you're done!
It's actually extemely quick, making this a very powerful tool!
See the Wiki Development List for ideas on what needs to be done.
A couple of other hints:
1. if you want the link text to be slightly different to the link name, use the pipe character. for example [[Ideology Geocaching|those fine dudes]] will display "those fine dudes" and link to our entry.
2. it understands plurals. if you write [[Cache]]s, it displays "Caches" but links to "Cache"
For more guidelines, see the Editing Help page