You must have the latest version of Java for this applet to work. To get the latest version of Java, go to http://java.com/en/download/manual.jsp and download the appropriate version.
IRC Commands

To change your nickname, type /nick [newnick]
To join a channel, type /join #channelname
To whisper/private message a user, type /msg TheirNick message you want to say
To quit IRC, type /quit