If you have one website, but would like to direct 2 or more domains to said site, you are free to do so! But before attemping to "point" your additional domains to your main site, be sure that you have (1) purchased the domain(s), (2) pointed the domain(s) to the appropriate server using the appropriate nameservers, and (3) added the additional domain(s) to your account. Now, complete the steps below:
Step 1: Login to your DirectAdmin account panel.
Step 2: Locate the section of the homepage that says "Advanced Features," and click on "Domain Pointers."
Step 3: Once there, you will see a text field that says "Source Domain http://www.________________ --> yourdomain.com eg: sourcedomain.com." in the blank text field, type in your domain name (without http://www. of course). So for celebfanatics, I would type in celebfanatics.net
Step 4: Ensure that the "Create an Alias" checkbox is checked, and click on "Add."
And voila! You can repeat this as many times as you want with as many domains as you want (you can't exceed 5 without paying a small one-time fee though).
You can apply this to subdomains as well! If you want a specific sub-domain to point to a domain, or an add-on domain in your account, follow the same instructions above substituting the domain for a subdomain!