After you have uploaded your site to your subdomain, you can then access that site in 2 ways - (1). You can access that site via yourdomain.com/cats or (2). cats.yourdomain.com. You CANNOT access your subdomain via www.cats.domain.com. Here the "www" is actually a type of subdomain in itself. So remember to setup all links to subdomains as yourdomain.com/cats or cats.yourdomain.com (without the www). Uploading to a subdomain ..../cats, will have the same Username and Password as your main site.