We invite everyone to contribute. Just pick a topic, write an article. Click on the "Edit text of this page" link at the bottom of every page to edit a page; for more information, see our editing instructions. The articles don't have to be long; a little bit in the early stages will help a lot. You can do so anonymously or give yourself credit. If you see an error, you can instantly edit an article to fix it.
Let's discuss the mechanisms of Wikipedia on Wikipedia policy (and in particular see the naming conventions page), and see the Wikipedia FAQ for answers to many questions.
You might be wondering: just why is Wikipedia so great, anyway?
If you've got a minute, think about publicizing Wikipedia. Think about leveraging effort--in the time it takes you to write two decent articles, you might be able to get ten people on board who can write ten decent articles apiece.