If you want a browser to be able to get to your site no matter what subdomain they requested (www.yourdomain.com or even anyname.yourdomain.com) without having set up specific directories or symlinks for those requests in advance, then you can use a catch-all subdomain to redirect their request for a non-existent, mistyped or random subdomain to a valid page on your website.
That's it!
If you have any questions, feel free to contact our Support Team.