I have confirmed that the statement below is true. This is the main url of halopedia: http://halo.wikia.com/wiki/Main_Page
To be able to create a new page, erase Main_Page and name it any way you want. For example you can type this url in your browser:
Where "NewPage" is the name you want to give to your page.
IMPORTANT:New pages are subject to approval by an admin. So I suggest you message an admin before you create a new page in a wiki.