Check your email and get the confirmation code. Now use the command:

/msg NickServ CONFIRM ConfirmationCodeFromYourEmail

The email should tell you this anyway, and you should just be able to copy & paste this whole command from it. This command automatically IDENTIFY's you, but in the future when you connect to Rizon you'll have to do this yourself using the command:

/msg NickServ IDENTIFY your_chosen_password