Search wiki for the term if the article doesn't exist then you will see an option to create one NOTE : If you are thinking about promoting your site then forget it.They will remove it as soon as they find it
As long as you can write an authoritative article on something useful then you can add a link to your site as a source (especially if your site content is good). This was a great strategy a few years ago, but links now have rel=nofollow tags so you get little link kudos, but people will still follow the links in the article. But your entry in wikipedia has to be good and your site (if you're linking to it) must be related and add to the article.
You can first sign up in wikipedia. There you can see an option for article submission. But you must be sure that your article is way too good to be published.
Why spamming? We have a very good written serious article, we already tried to put it but after some discussion it was removed. We guess between people that were against our article were our competitors Maybe you know another ways how we can publish it?
well it really depends on how you contribute to wikipedia. If you add interesting aspects at an article and that is related to your site you could add your link and it won't be removed. still, wikipedia has no-follow and it's a bit hard to get traffic from those links that appear in the footer.