To request membership in a project, click the Join This Project link on the Project Home page, which takes you to the Project Membership Request page. Users who are not logged into the domain, do not have permission to join the project or are already members of the project will not see this link. The radio buttons in the middle of the page present you with several role options. To select a project role, click on the radio button to the left of the desired role and click on the Submit Request button at the end of the list of roles.
Think of the roles as a method of informing the project owner of how you intend to contribute. You may request, or even be asked, to fulfill more than one role at some point, and you can certainly fulfill other roles on different projects. See more about project roles.
Depending on the project's configuration, you will receive an email from the project owner approving or disapproving your project membership. Upon being approved, you will also receive more information about the nature of the particular module you will be working on.
Once you are a project member and your involvement progresses, you may wish to change your role in a project. The Project Home page includes a Request New Project Role link in the top right corner of the same page you originally used to request membership originally in the project. Now, however, your current role is noted in the top section, and only the remaining roles available to you are displayed with radio buttons. Again, you submit this change as a request that the project owner must approve.
As a project member, you are able to work with the full set of hosted tools. These include signing up for tasks, reporting issues using IssueZilla, and obtaining project source code using CVS.