Your deployed application is available as
http://<appId>.<accountName>.cloudbees.net. This is fine for prototyping or test application, but you probably want to display your website to users with a better URL.
For mapping your domain name, the first thing to do is to buy a domain name. Although CloudBees doesn't provide this service, there are dozens of registrars available. To select one, just consider that you don't need any hosting option, as this is a common value-added service they offer, and instead need fine-grained control over your DNS.
As you get a domain name, you just have to configure your DNS settings (the way to do this depends on your registrar) to declare
www.yourdomain.com as a CNAME ...