All you have to do is create another site from our member interface.
- Visit the Sites panel.
- Choose "Create a New Site" from the "Actions" box.
- Add a "short name" for your site to use on our system. (You might be asked which account to assign the site to, if you have more than one eligible account).
- On the "Use another name?" screen, select the "Yes" button and use the text-entry field to the right of "If so, what is it?" to add your subdomain as an alias to your site.
You may also add additional subdomains to a site you already have, by following the instructions in this related FAQ entry.
We do not use or support the scheme of placing subdomains in subdirectories of your existing site that is employed by some mass-market hosting control panel options.