To install from an rpm package you can use "sudo rpm -Ihv <package file name>". I tend to use "sudo rpm -Uhv <package file name>". First check if the same package is available on your install disk or one of the FC repositories. Installing from a downloaded rpm can cause problems if the dependencies use different library versions, or the package may become locked and you could lose the benefit of automatic security updates.
If you downloaded the rpm from a livna repository or a similar unique Fedora Core repository, consider adding it as a source and then you can pick up updates from that site or use your graphical package manager to search for packages.