Repositories on fd.o take two forms: project repositories (e.g. dbus, cairo), and personal user repositories, which may contain anything. Project repositories are only available to projects already hosted on freedesktop.org.
Projects
If you want a 'project' repository on fd.o, file a bug with Bugzilla requesting a new repository. Include the name of the repository and a brief description. If you want commit notifications, please also state that, and let us know where they should go to.
Conversion using the parsecvs tool is also available: this has converted the X.Org, Cairo and XCB repositories, among others, mostly without incident.
Your repository will be available as ssh://git.freedesktop.org/git/projectname for commit access, and git://anongit.freedesktop.org/git/projectname for anonymous access.
Personal repositories
For personal repositories, SSH to people.freedesktop.org and execute:
mkdir repo-name.git GIT_DIR=repo-name.git git-init-db touch repo-name.git/git-daemon-export-ok vim repo-name.git/description chmod +x repo-name.git/hooks/post-update
You can now push into it from your local repository with: git push --force --all ssh://people.freedesktop.org/~username/repo-name
and it will be available from git://people.freedesktop.org/~username/repo-name; it will take up to ten minutes to be visible on gitweb.