Special:CreateWiki on the central Wikia is used to start a new wiki website on a topic that you want to write about. For example, if you were a Star Wars fan and there wasn't already a Star Wars wiki, you might add this to the form:
- Web Address
And then an almost blank wiki would be created at starwars.wikia.com for you to start creating the world best Star Wars encyclopedia!
Of couse, Wookieepedia already exists, so if you're into Star Wars, you can simply join them instead!
Have a look at the List of Wikia to see what sort of wiki sites other people are creating.