You need an IRC client (such as Xchat, for example) if you want to do this.
These are the steps followed to join a freenode.net channel, otherwise you’d be forwarded to a message saying “you must register your nick[name].”
1. Open the IRC client and type in /msg nickserv register … where … is your nickname
2. To login, type /msg nickserve identify … where … is your nick.
3. To add your email address, /msg nickserv set email … where … is your email.
4. Join a channel!