The default service name of NNTP is "nntp". You may, however,
have to define the service name as the number 119 as
follows:
(setq gnus-nntp-service 119)
If you'd like to use a local news spool of your machine directly
instead of NNTP, set the variable to nil as follows:
(setq gnus-nntp-service nil)
In this case, the NNTP server must be a local host name returned by the
function system-name (see section Using Local News Spool).