The change log usually appears at the end of a spec file and is marked with %changelog. It holds messages for each significant change. You should add a change log entry for each major change to the application. For example, if you download a new version of the software you are packaging, add a change log entry for the new version:

%changelog

* Fri Jun 21 2002 Bob Marley <marley@reggae.com>

- Downloaded version 1.4, applied patches

* Tue May 08 2001 Peter Tosh <tosh@reggae.com> 1.3-1

- updated to 1.3