I am working on a WordPress website and want to customize its domain name. The site owner originally set up the domain name through Vistaprint. He then bought the domain name from them, so it was released. In order to get it onto the WordPress site, do I have to REGISTER it through WordPress? Or is it somehow already registered through Vistaprint and I just have to map the existing domain name? Is it possible and/or cheaper to register the name somewhere else, instead of through WordPress??
I've already seen this: http://en.support.wordpress.com/domains/register-domain/
But basically, I don't know what registering a domain name means, or what I have to do next. Any help would be wonderful -- all of this stuff is relatively new to me.