Wikipedia is an open source, free online encyclopedia. For every article, there are several tabs, including discussion about the article, a history of edits, and the source itself. There are numerous articles from the Help Page which describe how to use, search, and edit existing articles and how to create new ones. (This page is also linked from the home page by clicking "Help" from the left hand menu.)
A friend who is one of many -- I think several hundred -- moderators on the site told me that that material on ballet is weak, and the Wikipedians would appreciate contributions to the site on the topic. If you are interested in contributing, there are a few things you should know:
1. Articles are subject to revision by the entire community. While there are moderators who are on the lookout for gratuitious and spiteful edits, it can be frustrating to have to negotiate or justify content in discussion. They have a long and arduous arbitration process for "re-educating" and removing posters who would be shut down on Ballet Talk in several seconds flat. Like any community, getting a feel for how it works -- reading the discussion pages is a good start -- before jumping in is a good strategy, and the more reasonable, respectful, and knowledgeable posters are recognized fast and get the support of the core.
2. It is an encyclopedia, and it aims for facts, claims and information that are proportional to their importance in the issue, particularly in the opening and summaries. Citations are particularly important, and uncited material may be edited out or quarantined, to be reinstated when a citation is added. Gushing is usually edited out quickly. (The Michelle Kwan article comes to mind.) An entire article about a young soloist at ABT, for example, would be cut in all likelihood and perhaps edited into a general article about a new generation of dancers.
3. Contributors are welcome to translate existing articles in other languages to English and vice versa. The list of languages supported in Wikipedia is on the main page in the left hand column.
4. Whether a person or event is considered important enough to belong in an encyclopedia determines whether an article should be linked from a main article -- for example, if I mentioned a current PNB dancer in an overview article on the history of ballet, the reference would be removed -- or is a fan article, which would be removed. Putting a dancer in context helps to establish why a dedicated article should be there in the first place, particularly since ballet might not be an area where the moderators have a lot of experience. For example, many might not have heard of Alicia Markova or Alexandra Danilova any more than I would know who influenced rock music.
The main aspect of Wikipedia is that it is a collaborative effort.