To connect to a New Server you have to do the following;

1. Press the New Server button on the Start tab on the chat.

You get this:

2. Type in the command /server (servername) which will connect to that server.

Like this:

3. After you press enter it connects to the server like this:

4. Now you are all set to use the new server and you can join channels by using the /join #channel name command.