Detailed instructions on Trac in general and the Wiki specifically are available in your Trac under the topic TracGuide. You can reach this topic by going to the Help/Guide link in the upper right of your Trac home page, by adding /wiki/TracGuide to the path to your Trac instance. Once there, you can find instructions on the wiki under the topic TracWiki.
If the help documentation provided by Trac is not clear, you are always welcome to file a ticket and we will try to answer your question as quickly as possible.