It’s very easy to edit the content of a MediaWiki page, you just need to click the “Edit” page tab at the top of the page then make changes to the content and click click the “Save page” button. Moreover you may use the “Show preview” button to see what your change look like, before you really save them to go live. Easy as that! The tricky part is editing rules, editing conventions, and formatting.
There are several ways of creating a new page on any MediaWiki website. Such as you can create new pages by following red color internal links, you can create new pages via search box etc. It depends on what the admins have configured on the wiki to produce.