Slash-join, space pound-channel (/join #channel) connects you to that channel.
Slash-invite space nick space pound-channel (/invite nick #channel) invites the user to follow you to the channel specified.
Slash-list (/list) lists all current channels. You can add a min number and max number, which will show channels with a minimum and maximum number of people.
Slash-leave space pound-channel (/leave #channel) disconnects you from that channel.
Slash-quit (/quit) disconnects you from the server, and any channels you might have been using.
Slash-away space message (/away message) will send a message to anyone who tries talking to you while you're away.
Slash-nick space nickname (/nick nickname) changes your nickname to a new name.
Slash-query space nick (/query nick) opens a private message window where only you and the person you query can talk.
Slash-whois space nick (/whois nick) shows information about the user.
Connect brings you to the default chat server you have selected.
Disconnect closes the connection to the IRC server.
Setup Information brings up a window that allows you to configure IRC servers and your identity.
General Options displays a window that allows you to configure many user options.
Channels folder displays a list of frequently-used channels.
List Channels opens a window you can use to search for channels.