All members are allowed to edit pages in the Open Source Photography wiki. So, after you join the site and login, simply click on the edit link at the bottom of each page. This will open an editor with a toolbar palette full of options. Edit and save. That's it.
To create a link to a new page, use syntax: [[[new page name]]] or [[[new page name | text to display]]]. Follow the link (which should have a different color if page does not exist) and create a new page and edit it!