Go back to your account panel and click on Hosting at the top. Scroll down a little and then click on the "Login to cPanel" button. You should now be in your cPanel. Look for the domain buttons that say Addon Domain and Parked Domain.
If you want do to a completely different site, then click on Addon Domain, and choose what you want for a new domain like when you first signed up for an account. This will create a subdomain directory for you to put your new site in. You'll find that new directory/folder inside your root folder when you look in the file manager. The name of that directory will usually be the new domain name that you chose.
But if you want another domain name that goes to the same site as your main domain, then click on Parked Domain instead, and choose what you want for a new domain like when you first signed up for an account. Make sure that it's pointed to your root directory.
