The Manual of Style is a short primer describing the rules and policies for creating and writing Wiki articles on the site. The short collection of pages also covers Wiki formatting and site rules.
Words of advice: Just edit, and use your best judgment! In other words, add helpful information and use good grammar, and you'll be just fine.
You may read Wiki Formatting Help to learn how to format your text, and maybe the Rules to know what to avoid, but honestly? If you've got information to add, just start editing!
A complete table of contents can be found in Category:Manual of Style.