vladkrack is right, you need the rpm-build package installed (which you probably have). There are many ways to do it, but the method I use to build source RPMs is:
rpm --rebuild foo.src.rpm
Where foo is the name of whatever the source RPM is. If all goes well (and you don't see it bomb out with error messages), it'll compile and build the binary RPM (sometimes more than one) and save it somewhere. Look for a line towards the end of the output that says "Wrote file /usr/src/RPM/RPMS/i386/foo-i386.rpm." From that point, all you gotta do is install that RPM normally, like so:
rpm -ivh foo-i386.rpm
There are other options that come in handy. One I like to use, since I never plan on using these RPMs on any machine other than this one, is the target option. For example:
rpm --rebuild --target athlon foo.src.rpm
This makes it build with optimizations specifically for the AMD Athlon. See the rpm man page for more information. Good luck!