I love basic questions, they're easy to answer!
First of all, determine your IP address. That is the "public" IP address of your home router, which is the only address that is reachable over the Internet: http://whatismyipaddress.com/
If you're not paying your ISP extra, it is probably NOT a static address. This means it might change from time to time, and if you want people to be able to connect to a server in your house, you need to provide a static DNS name for them to use to connect. You can accomplish this using DynDns: http://www.dyndns.com/services/dns/dyndns/
Finally, you need to get incoming traffic from your router to your computer. This involves configuring your router to "port forward" incoming Port 80 traffic to Port 80 on your PC. For guides on how to configure port forwarding on your router: http://portforward.com/
Hope this helps, if you need any specific details post a comment.