A subdomain is a subdivision or branch of a domain. It is created by adding a prefix to the main domain name, separating it with a dot (.) For example, blog.example.com is a subdomain of the domain example.com. Subdomains are typically used to organize and categorize different sections or functionalities of a website.

An addon domain, on the other hand, is a separate domain that can be hosted within the same hosting account as the main domain. It allows you to manage multiple domains and websites from a single hosting account, each with its own content and settings.

To set up a subdomain in cPanel, follow these steps:

1. Log in to your cPanel account provided by your hosting provider.
2. Navigate to the "Domains" or "Domains" section.
3. In the "Subdomains" section, click on the "Subdomains" option.
4. Enter the desired prefix for your subdomain in the "Subdomain" field. For example, if you want to create a subdomain called "blog" for your domain "example.com," enter "blog" in the subdomain field.
5. Choose the domain you want to create the subdomain for from the drop-down list.
6. The "Document Root" field will automatically populate. This specifies the directory where the subdomain's files will be stored. You can leave it as the default or modify it, if needed.
7. Click on the "Create" button to create the subdomain.

To set up an addon domain in cPanel, follow these steps:

1. Log in to your cPanel account.
2. Navigate to the "Domains" or "Domains" section.
3. In the "Addon Domains" section, click on the "Addon Domains" option.
4. Enter the desired domain name in the "New Domain Name" field.
5. The "Subdomain" and "Document Root" fields will automatically populate based on the entered domain name. You can modify them if needed.
6. Enter a password for the addon domain in the "Password" field. This password is used for FTP access to the addon domain's files.
7. Click on the "Add Domain" button to add the addon domain.