You can use cPanel to easily add a new domain to your hosting plan (if supported by your plan). Once the domain is added, you must simply point the domain at the following name servers:
FREJA.NS.WPOPT.NET
SAGA.NS.WPOPT.NET
Once these two steps are done the domain will start resolving to the designated folder within your hosting plan and you can then either set up a new site under the domain, create redirects for the new domain to an existing site, or create email accounts etc.
To add a domain (called "addon domain" to your account, perform the following steps:
1) First, start off by logging into cPanel and clicking on the section entitled "Addon Domains"
2) On the following page, simply enter the new domain name (without the http:// and the www.). The other boxes will auto-populate and generally can be left as they are unless you specifically wish to change the location where the new domain will have its files, or its new subdomain (i.e. how it will interact in conjunction with your main domain name - for example, it would normally be reachable at both new-domain.com and new-domain.main-domain.com)
3) Simply click "Add domain". When your name server changes for the domain have propagagted it will resolve to the new environment.