First off, this is not a very good way to host a website, due to the limitations of a home broadband connection, as well as some security concerns.
That aside, there are a few steps to follow:
1. Your domain name must be pointed at your public ip address (the one on your router, usually provided by your isp*)
2. The router must be set to forward http (and perhaps https) traffic to your web server (look in the manual for your router for this, it is usually quite easy).
* The problem with this part is that you probably have a dynamic ip address. While you can ask your isp for a static one (that doesn't change), they will most likely charge you for it. As an alternative you can look at ddns (
http://www.dyndns.com/) which tracks your ip for you and keeps the name pointed at it.
Have fun!