If you have a slow machine, or are just really impatient, there are a few things you can do to make Gnus run faster.
Set gnus-check-new-newsgroups and
gnus-check-bogus-newsgroups to nil to make startup faster.
Set gnus-show-threads, gnus-use-cross-reference and
gnus-nov-is-evil to nil to make entering and exiting the
summary buffer faster. Also see Slow/Expensive Connection.