Your system may currently have the rpm command but not the rpmbuild command. (If the command "which rpmbuild" does not display anything, you don't have rpmbuild.) On Red Hat and Fedora systems, the rpmbuild command is provided by the rpm-build RPM package. (You can give the command "rpm -q rpm-build" to check if it is installed.)
Install the .src.rpm file this way:
rpm -i somepackage-1.0-1.src.rpm This will create files in the SOURCES directory of your RPM building directory tree, and a .spec file in the SPECS directory.
Then go the SPECS directory and give the command to build the RPM:
cd /home/your_userid/rpm/SPECS rpmbuild -bb somepackage.spec Give the -ba option instead if you also want to build the SRPM. The binary RPM packages will typically be created in the RPMS/i386 directory (on a PC-based system).