You should have received an email with a link to your control panel after you completed your nation install. Note that you can't access your control panel until you have finished installing your nation. If you didn't receive the email, you can just add /admin to the end of your nations URL to access the control panel. So if your nation URL was http://juarita.nationbuilder.com, you would go to http://juarita.nationbuilder.com/admin.