Finally don't worry, you can't accidentally break anything. Every change to any page is backed up and can be restored if something goes wrong. We also keep regular backups in case of disaster or someone malicious finds and exploits a bug. This means you can't seriously damage a page by mistake and it also means that anything that you contribute to the site can't be lost or deleted by someone else.
See also: AboutWiki
Here is a list of all the pages which belong to this category, they should teach you most of what you need to know to find your way around this new home.