Channels are based roughly on the irc model. Here's a summary 
of the commands (there's also help on the individual commands):
  @makechannel foo  -- Create a (public, unmoderated) channel named foo
  @joinchannels foo  -- Join channel foo (which must be public)
  @leavechannels foo -- Remove yourself from channel foo
  #foo hi
  #foo ..inky yo    -- talk on channel foo
  #foo :cries!
  ;meep             -- talk on the last channel mentioned   

  ALSO: see 'help channel-aliases' for ways to shorten channel names

  @statchannel foo -- Print info on channel foo
  @listchannels    -- List all public channels

  @mutechannel foo -- gag/ungag a channel temporarily without leaving it

  The following commands require you to be a channel pope on the

  @topicchannel foo = This is the foo channel -- Set topic for channel foo
  @flagchannel foo = private   -- Make channel foo private 
  @flagchannel foo = inky : pope -- Make inky a channel pope on foo
  @addtochannel foo = inky     -- Make inky a member of private channel foo
  @remfromchannel foo = inky   -- Remove inky from channel foo
  @delchannel foo              -- Delete channel foo, removing all its members
  @renamechannel foo = bar     -- Changes the channel's name to bar

  If there are no popes on the channel, type @popeme to become one.

  The new channel-category system adds the following wizard-only commands:
    @makecategory games/cards  -- Creates category games/cards
    @delcategory  games/cards  -- Deletes category
  More generally, you can also refer to channels by their full name:
    #games/cards/poker Do you like dogs playing poker?
    @rename #games/cards/poker = #homes/fireplaces/tools/poker
    @listch games              -- Lists everything in the games category