If you have a specific problem it's best to ask about it
on the users' or developers' mailing list. There are tons
of options but (almost) all of them are set to reasonable
defaults. Usually, the only thing you really need to configure is adding the paths to directories with files you
want to share. If the tooltip for a setting doesn't look
interesting or you don't understand what it's about it's
rather likely that keeping it as-is is perfectly fine.

One thing that's interesting but a little difficult is the
filter system. However, you'll find a link to a short tutorial on the website:

http://gtk-gnutella.sourceforge.net/index.php?page=docs