The prep section, short for prepare, defines the commands necessary to prepare for the build. If you are starting with a compressed tar archive (a tarball) of the sources, the prep section needs to extract the sources.

For example:

%prep

%setup -q

The prep section starts with a %prep statement.

This example uses the %setup RPM macro, which knows about tar archives, to extract the files. In most cases, this will be all you need in your spec file prep section.