Ok so if you have a domain name say... domain.com, I assume that you would want your visitors to access your web site via the host name... www.domain.com. So, most registrars also provide DNS management. DNS is the system for mapping host names to IP addresses. If your registrar provides you with management over your DNS zone, you would create a host record called "www" and point that record to the public IP address that the web server will be using.
If this web server is on your private network, you would have to map the DNS record to the public IP address of you router and on the router, create a port fowarding rule to map the public IP to your private IP on port 80 (HTTP) and/or 443 (HTTPS).
If this website is for testing/enjoyment, that's fine. However, if this is for production/business, you may want to reconsider hosting the web on your server. The main reason is that it is going to be challanging for you to provide a highly reliable web site service on a consumer based network using one server (no offense...). Your network link is most likely Async which means your download and upload pipes are significantly different. Your upload pipe is going to be your vistors' download experience. So if you have 5 mb download but only 384 kb upload, your visitors are not going to be impressed with your network connection. In addition, you'll find it challanging to keep one Windows server up and running 100% of the time.
Its fun to do this at home especially for learning (ive done this myself many times..) so I am not trying to discourage you in any way.