Subdomains and zone files

Hello all, I am a newbie here (and to server setup in general), but I have hit a roadblock with my Mac OS X Server. I am hosting over a DSL connection, so I gave my ISP the info concerning my domain name and IP, they do my dns, and everything works super. So now I want to setup subdomains, (i.e. subdomain.mysite.com), and route them through to different folders on the server. How do I accomplish this? I bet I will have to setup a zone file, can I then use that to point to a certain folder in the directory tree? I realize this a tall order which is vague on the details, but I am a quick learner, and I would appriciate and assistance you could offer. Thanks in advance. -- whit