If you're using the QuakeNet network, you need to have
registered an account with Q, "/msg Q hello" then auth
each time you connect.

That should allow you to join +R (authed users only) channels.

http://quakenet.org/faq/faq.php?c=176&f=177#177

If you're not using QuakeNet, then as the first reply suggests...
read the help for your IRC network smile