1. Click Domains icon here.
2. Click on the domain for which you want to create a subdomain
3. Click Subdomains icon here.

4. Click Create Subdomain option.
5. Now enter the prefix of the subdomain you want to create
6. Select SSL support check box if necessary.
7. You can create a separate FTP user account for this subdomain if you wish to restrict the access from the main domain.
8. Select the services to be supported for this new subdomain.

You have successfully created a subdomain.