It takes a little bit of work but it is simple once you got it 🙂
I understand your webserver is up and running since you proved that.
Next would be to get a dynamic DNS setup - I personally use www.dyndns.org and they also got a free updater which is easy to use. When that is done you need to actually tell your router what to do with incoming web packet requests so logon to the router and create a "port forward" for port 80 and then point it to the IP of your server (each router is different but setting should be easy to find. Sometime referred as virtual server etc).
Basically:
1. Setup dns name so computers on internet can actually find your site
2. Setup port forward for på 80 on your router -> your webserver. Otherwise router will just discard incoming request
You can see if port forward works by going to your internet IP instead of hostname (if you got problems and need to see if its a routing or DNS issue)
Hope I make some sense 🙂