Addon domains are handled in a similar way to subdomains in regards to the file structure listed in your file directory. However, the addon domain URL appears like a primary domain. In general, nothing that happens in your addon domain's files or DNS should affect the rest of your domains.
While addon domains do not have their own cPanel, you can still perform actions you normally would for your primary domain such as create email accounts, sub, redirects, view website statistics, etc.
Addon Domain URLs
Every addon domain is also a subdomain as a result of this, you can load your addon domain using any of the following URLs:
As an Addon Domain
As a Subdomain
As a Subfolder