At startup, GNUS reads your `.newsrc' news initialization file and attempts to communicate with the local news server, which is a repository of news articles. The news server need not be the same computer you are logged in on.
If you start GNUS and connect to the server, but do not see any newsgroups listed in the Newsgroup buffer, type L to get a listing of all the newsgroups. Then type u to unsubscribe from the newsgroups you don't want to read. (You can move point to a particular group using n and p or the usual Emacs commands.)
The first time you start GNUS, it subscribes automatically to every newsgroup that exists. Subsequently, GNUS subscribes automatically to all newly created newsgroups. You can unsubscribe groups with u. You can inhibit automatic subscription by adding the following line to your `~/.newsrc' file:
options -n !all !all.all
When you quit GNUS with q, it automatically records in your `.newsrc' initialization file the subscribed or unsubscribed status of all newsgroups, except for groups you have "killed". (You do not need to edit this file yourself, but you may.) When new newsgroups come into existence, GNUS subscribes to them automatically; if you don't want to read them, use u to unsubscribe from them.