Overview
An addon domain allows a new domain name to link to a subdirectory of your account. The addon domain’s files will be stored in a subdirectory of your public_html (Document Root) directory. Addon domains allow you to control multiple domains from a single shared hosting account. Addon domains are allowed by your web host in WHM's Tweak Settings interface. (Home >> Server Configuration >> Tweak Settings).

Video Tutorials >> Learn about creating and managing addon domains. Quality: High | Low

Create an Addon Domain
To create an addon domain:

Log into your cpanel account and click Addon Domains

Enter the domain for the new addon domain in the New Domain Name field.
Note: When you enter the domain name, cPanel automatically populates the Subdomain/FTP Username field. If you are creating multiple addons with similar domain names (differing only in .com, .net, etc.), be sure to manually enter a unique username into theSubdomain/FTP Username field.
Enter the directory that will contain the addon domain’s files in the Document Root field.
Enter the password for the addon domain into the Password field.
Make sure you use a secure password.
You can have cPanel generate a secure pasword for you using the Generate Password feature.
Confirm the password in the Password (Again) field.
Click Add Domain
Note: When you create an addon domain in the cPanel interface, cPanel automatically creates a subdomain. If you alter or delete the subdomain after it has been created, you may affect or delete the information displayed in the addon domain's website.