The Congress wiki page is the authoritative starting point.
https://wiki.openstack.org/wiki/Congress
If you would like to contribute to the development of any OpenStack project including Congress, you must follow the steps in this page:
http://docs.openstack.org/infra/manual/developers.html
Once those steps have been completed, changes to OpenStack should be submitted for review via the Gerrit tool, following the workflow documented at:
http://docs.openstack.org/infra/manual/developers.html#development-workflow
Pull requests submitted through GitHub will be ignored.
Bugs should be filed on Launchpad, not GitHub:
https://bugs.launchpad.net/congress