Colloquy is an IRC client for Mac OS X available here.
To get into E-shuushuu's IRC channel, you need to set up the connection:
- Launch the client
- Go to "File > New Connection"
- Fill the different section as in the screenshot. Replace <your nickname> with yours. To add the channel, press the "+" button at the bottom. A field will appear where you can add "#e-shuushuu", then press enter.
- Finally, click on "Connect"