Welcome to the Wiki Guide.
There are two ways of editing a page. Either by improving it, or by asking questions (maybe something is not clear to you).
You can improve a page by simply clicking on a edit link. There are edit links for each section in a page, and an edit tab at the top for editing the complete page. Editing should only be done if you can improve the information on the page.
If you think that something is unclear or ambiguous, use the discussion page instead (discussion tab). This will create a new page where you can ask questions or just give feedback on a page.
Both of these methods are most welcome since they will eventually lead to a much better documentation.
First off, you should read the following page: How to edit a page
Or if you just want to see the wiki syntax: Wiki CheatSheet