Join is the command used to join a channel. It has the following format.
If the channel has a channel key, the following command must be used.
/join #chan channelKey
If joining multiple channels, WITHOUT channel keys, in a single commandline statement:
/join #chan1, #chan2
If joining multiple channels WITH channel keys in a single commandline statement:
/join #chan1,#chan2 key1, key2
If the channel is invite only, use the following command and wait for another user to send an invite.
/knock #chan Message to channel ops.
If the user is banned, I am banned is hopefully helpful.