Does the address start with 10., 192.168., or 172.18.?
If so, those are private, non-routed ip addresses; they're reused for many closed networks. Some device upstream from you is translating those into real-world, routable addresses, which is how you're getting to the internet.
You'd need:
1) to have that device configured to translate in the other direction, so port 80 on some real-world address gets handed over to port 80 on your machine--this may already be the case;
2) to know what that real-world address is, and have people outside your local network use it to reach you.