So you want to use IRC from Barnowl? Excellent!
Then you can use barnowl commands such as
----> /msg -a freenode #barnowl Hi everyone! I'm trying out IRC on barnowl!
The usual message commands such as "r", "R", "i", etc. should work. If you want to see the IRC commands and variables, use :show commands and :show variables and look for the ones starting with "irc-" and "irc:". In general, the command /foo in a traditional IRC client is :irc-foo in barnowl.
:set irc:spew if you want a bunch of admin messages when you get unhandled IRC events from the server. Not many of these are still useful, but if a command is supposed to get you output and you don't see it, this is something to try.
Ask geofft or -c barnowl if you have questions about getting it working.