We are happy to understand that you are enjoying our services, and you are expanding your domain pool. Our system aims to point your domain name automatically to the respective hosting account when you purchase it. However, our system has no way of knowing what the purpose of this domain is, thus it is not going to take any actions other than pointing it. Some of the reasons you purchase a domain name could be to build a website on it, park it on your current primary domain, redirect it to a different domain for increased SEO, or use it for a business email. To utilize it as intended, you need to create a DNS zone for it by adding it to your cPanel.
We have great tutorials about how to park a domain and how to add an addon domain in cPanel.