This is a website for the developers of Wikimedia wikis (that means a number of well-known wikis) to test their latest coding. This site is a "testing area" of sorts, which allows code to be tested in a controlled environment, without damaging other wikis. This wiki can also be used as a classroom to teach basic wiki editing without damaging other wikis.
This is not Wikipedia or any other content wiki—for them see the list on the Main Page—but rather a testing ground for developers. There's not much you can do here unless you're testing code; if you're looking to contribute content, you may wish to visit one of the Wikimedia Projects.