When you create a subdomain you need to set a document root for the subdomain
If you want to set a subdomain like blog.yourwebsite.com, please use as document root something like public_html_blog; where yourwebsite.com is your domain. All content for the respective subdomain must go in this folder in order to be displayed
Use the steps above in order to create whatever type of subdomains you want
The subdomain feature is provided inside cPanel and in this page is documented how to create a subdomain from cPanel.
Please note that cPanel services are required
If you do not have cPanel services please contact your sales representative