you'll wanto to make sure that the XChat Aqua icon/folder is now somewhere on your hard drive. You do this by mounting the .dmg file that you downloaded, then dragging the directory into your Applications folder.
After everything has been transferred to your hard drive, you need to open the XChat Aqua application. when this is open you will do the following:
File --> Server List (or Command S)
The Server List is Alphabetized, so scroll down to the E section and Select
"EFnet", and fill out all of the personal information at the top of the
screen <Nick name, Second Choice, etc.>
Click Connect when you have filled out all required information and selected EFNet.
You will now have a plain chat window that runs through all the connection mumbo jumbo until it is connected to the EFnet server. When it has connected you will:
User Menu --> Join Channel...
You will be prompted to choose a channel to join, and you will enter:
This should do the trick.
EDIT: I just went through and connected to verify my instructions. It took me a bit of time to connect to the EFnet server, but if you leave the app alone and let it do whatever it does, it will connect you. Just let it get through all the stuff that it has to spit out when it connects you, and then do the User Menu --> Join Channel... #flyingspaghettimonsterism
It takes 47 muscles to frown and 13 to smile,
but it takes 0 to sit there with a dumb look on your face.