To add a web hosting (cPanel) account in WHM, after logging in, click Home » Account Functions » Create a New Account
Fill out the requested fields displayed and choose a package template (For info on how to set up packages, see https://secure.entitydata.com.au/index.php?rp=/knowledgebase/29/How-to-set-up-disk-and-traffic-limits-using-Packages.html)
In DNS settings check 'Use the nameservers specified at the Domain's Registrar (ignore locally specified nameservers)', if you have not set up the virtual server as a name server and are hosting DNS elsewhere.
In Mail routing settings, check 'Remote Mail Exchanger', if you do not intend to use the server to host mail for the domain you are setting up.
All other options can be left as their defaults.
Click 'Create' and you're done.