If you download an RPM its installation instructions (if there are any) will tell you to install the packge via

rpm -ivh rpm-file

This will work if the RPM has no further dependencies. But if there are some dependencies RPM will complain about missing libraries. Now you have to determine which package(s) you need to install to get these libraries.
The eeasy way is to use YUM to install the package:

yum --nogpgcheck localinstall rpm-file

YUM will take care about the prerequisites and install them for you.