Public Chatting on IRC

Public Conversations

We previously learned how to find channels using the /list command. Here will talk about how to join those channels and talk on them.
There can be many thousands of channels on the largest networks, each with anywhere from one to hundreds of people. Each channel is controlled by channel operators or "ops" who have absolute authority over their channels. We will discuss more about that later. You should always observe basic netiquette when visiting other people's channels.

/JOIN #channelname

Changes your current channel to the channel specified. If the channel does not exist already, it will be created and you will be in charge of the new channel and be a channel operator or "op" - more on that later.

/JOIN #new2irc
*** YourNick (foo@hot.school.edu) has joined channel #new2irc
*** Topic for #new2irc: New users welcome! Questions answered with a smile! ;)) RC
*** Topic for #new2irc set by Otiose on Sun Aug 16 10:28:06 1998
*** Users on #new2irc: YourNick FunGuy @pixE @MsingLnk @^Chipster
    [rest of list truncated]

When you join a channel, everything that everybody says is preceded by their nicknames so others can tell who is saying what. For some IRC programs, it doesn't show your own nickname, but don't worry, other people still see it! You type: hello world! but everybody else sees: <YourNick> hello world!

/ME does something

Performs an action on a channel. Unlike talking normally, actions do not start with <YourNick>. Use /ME in the third person (verbs like "is", "does", "runs", etc.).

/ME is a pink bunny

YourNick is a pink bunny

/LEAVE [#channel_name]

Leaves the specified channel, or if no channel is specified, leaves the current channel.  

source: http://www.irchelp.org