Articles can be added by anyone, as far as I am aware. If you take a look at the articles which currently exist, you can see what kind of information they contain and the format they are written in.
If you want to write an article, I would definately advise refining it in the forums first before posting it. I would also advise that you ensure that everything it contains is accurate and factual, preferably with pictures and fully referenced if that is required.
The article turorial may help you