Welcome to the forums!
If you are brand new, then why are you using Fedora 12? It is no longer supported and receives no security updates or bug fixes. Fedora 15 is the current release, available here: http://www.fedoraproject.org
To answer your specific question, if you are out of free space, then you need to make some free space.
Delete files you no longer need, empty the Trash, etc. You can also try "yum clean packages" to clean up any cached packages. "man yum" will tell you more.