The sys file, located in /usr/lib/news, controls which hierarchies you receive and forward to other sites. Although there are maintenance tools named addfeed and delfeed, I think it's better to maintain this file by hand.
The sys file contains entries for each site you forward news to, as well as a description of the groups you will accept. An entry looks like
Entries may be continued across newlines using a backslash (). A hash sign (#) denotes a comment.
When setting up C News, you will most probably have to write your own sys file. To help you with it, we give a sample file for vbrew.com below, from which you might copy what you need.