If you don't already have Textual installed, you can download it from the App Store. You can also compile it from source which is available at GitHub.

When you open Textual the first time it starts a connection wizard. You can skip it and add a new connection from Server / Add Server... menu in the OS X status bar.

Enter the following settings:

• Settings

  Organization:
• Network name: Your organization name
• Primary Server: <orgname>.irc.grove.io
• Port: 6667 (for SSL use 6697)
• Server password: Your organization name (not your password)
• Nickname: Your username
• Username: Your username
• Nickserv Auth: Your password

After creating a new server, connect to server and Textual will join channels automatically.