There are a couple steps you must take to get a website up and running. First, you need to register for a Domain Name, if you have not already. This can take a few days, so do it early. Even this takes a number of steps.
Second, you'll need a fixed IP address. Depending on what your application is, this can either be on your intranet, or on the internet. If you want the whole world to access your server, it has to be on the internet, and not behind some Cable/DSL router using IP masquerading.
third, you'll need someone to provide DNS for you. You can do this your self (though I'm not 100% sure if DNS & Bind are implemented in the 'standard' way on OS X), or through your ISP. It's always a good idea to have a backup DNS server (a 'secondary'). So you could use your machine as primary, and your ISP as secondary.
Lots of these things require that you register them through Network Solutions, or another Internet Registry.
- YOU need to be registered, first of all. They need some way to contact you for various issues about your domain.
- Your DOMAIN needs to be registered. Here, you tell the registry what your site is, who is responsible, and what server is the authoritative DNS server.
- Your DNS SERVER must be registered, if you maintain your own. This needs to have it's own IP address (though it can be the same as the web server).
Getting the actual Apache server up & running on your Mac is the easy part. At least for a standard implementation. If you want to run multiple websites, that's another matter, and requires knowledge of teh administration & configuration of Apache and Mac OS X.
Hope this helps!