Ladybow,

The real question is "why" before how.

I'm a fan of Suze Orman. Often she tells someone, "Yes, you could, but why would you want to?"

Subdomains have some good uses. Often they are used for blogs, for example. You see the address: blog.yourdomain.com, for example.

If you have a use like that OK but in general you have better navigation for getting people where you want linking through your site in the normal way with folders. If you ever need a subdomain you will probably know it.

Good Success!

James