If you are not a developer, the wiki and issues will be most useful.
If you are a developer, login with a GitHub account to access more features. The links under MANAGE will be most useful, but there are many more interesting utilities (feel free to look around). Assigned Tasks below shows all tasks assigned to you (select one of the tabs to see only tasks of the specified priority). To do anything but look around, email webmaster@clusterlabs.org and ask to be added to the Developers group, which can create projects and tasks.
This site is an instance of Phorge.