First of all, you should know that there is a special buffer called *Server* that lists all the servers Gnus knows about. You can press ^ from the Group buffer to see it. In the Server buffer, you can press RET on a defined server to see all the groups it serves (subscribed or not!). You can also add or delete servers, edit a foreign server’s definition, agentize or de-agentize a server, and do many other neat things. See Server Buffer. See Foreign Groups. See Agent Basics.
The gnus-select-method variable says where Gnus should look for
news. This variable should be a list where the first element says
how and the second element says where. This method is your
native method. All groups not fetched with this method are
secondary or foreign groups.
For instance, if the ‘news.somewhere.edu’ NNTP server is where you want to get your daily dosage of news from, you’d say:
(setq gnus-select-method '(nntp "news.somewhere.edu"))
If you want to read directly from the local spool, say:
(setq gnus-select-method '(nnspool ""))
If you can use a local spool, you probably should, as it will almost
certainly be much faster. But do not use the local spool if your
server is running Leafnode (which is a simple, standalone private news
server); in this case, use (nntp "localhost").
If this variable is not set, Gnus will take a look at the
NNTPSERVER environment variable. If that variable isn’t set,
Gnus will see whether gnus-nntpserver-file
(/etc/nntpserver by default) has any opinions on the matter.
If that fails as well, Gnus will try to use the machine running Emacs
as an NNTP server. That’s a long shot, though.
However, if you use one NNTP server regularly and are just interested in a couple of groups from a different server, you would be better served by using the B command in the group buffer. It will let you have a look at what groups are available, and you can subscribe to any of the groups you want to. This also makes .newsrc maintenance much tidier. See Foreign Groups.
A slightly different approach to foreign groups is to set the
gnus-secondary-select-methods variable. The select methods
listed in this variable are in many ways just as native as the
gnus-select-method server. They will also be queried for active
files during startup (if that’s required), and new newsgroups that
appear on these servers will be subscribed (or not) just as native
groups are.
For instance, if you use the nnmbox back end to read your mail,
you would typically set this variable to
(setq gnus-secondary-select-methods '((nnmbox "")))