In your Control Panel, you will see a section called "Domains", which includes options for Subdomains, Addon Domains, Parked Domains, and Redirects - here is a guide to the differences between them!
Subdomains are URLs for different sections of your website. They use your main domain name and a prefix. For example, if your domain is yourdomain.com a sub-domain of your domain might be support.yourdomain.com.
An addon domain allows visitors to reach a subdomain of your site by typing the addon domain's URL into a browser. This means that you can host additional domains from your account, if allowed by your hosting provider. (Portfoliositez DOES allow this)
Parked Domains (Domain pointers) allow you to "point" or "park" additional domain names to your existing hosting account. This will allow users to also reach your website when entering the "parked" or "pointed" domain into their browsers.
Redirects allow you to make a specific web page redirect to another page and display the contents of that page. This way you can make a page with a long URL accessible by a page which has a shorter and easier to remember URL.