When you install a src.rpm, you get a minimun of two files installed; more if there are patch files in the src.rpm. The location of the installation varies among the distros. To find yours, open a terminal and do 'locate SPECS' (without quotes). That is where the src.rpm will install the spec file which will build the new binary rpm. Then 'locate SOURCES). That is where the src.rpm will install the source tarball and patch files. To build a new rpm, cd to the SPECS directory, and, as root, issue the command 'rpm -bb <filename>.spec'. -bb tells rpm to build (-b) and binary (b) rpm. Substitute the filename of the spec file for <filename>. When it's all done cranking, you will have a new, installable rpm in the RPMS directory, in one of the subfolders, which you can install (unless more errors crop up).
See the manpages on rpm for more info on building rpms.