A WikiProject is a project to manage a specific topic or family of topics within Wikipedia. It is composed of a collection of pages and a group of editors who use those pages to collaborate on encyclopedic work. It is not a place to write encyclopedia articles directly, but a resource to help coordinate and organize the writing and editing of those articles.
The discussion pages attached to a project page are a convenient forum for those interested in that project.
WikiProjects welcome new participants; please feel free to join any or all that interest you!
Before starting, read the guide to WikiProject organization, and peruse some existing WikiProjects to understand how they operate "in the wild". If you're not sure about creating a new project, or aren't certain if anyone else is interested, you can make a WikiProject proposal; like-minded editors may start new WikiProjects at any time and are encouraged, but not obligated, to propose them before doing so, as they may thus receive valuable input and save a lot of work.
For additional resources, or if you have any questions, please visit the WikiProject Council or see List of Wikimedia projects for details.