Make Ubuntu Server Accessible to the Internet

"Usually, a home network consists of an internal computer(s) connected to a router or gateway, which connects to the ISP, then the world. In a logical sense, once you get outside the router or gateway, you're visible to the world. So, you would need to access the router or gateway and forward ports from your specific machine's internal IP address to the world. There's really 3 steps that makes this an efficient setup:

An internal reserved or static IP so the forward rule always works.
A rule to forward the ports you need through the router to the world. If you're running a web server, then just 80 would suffice.
A dns name pointing to your machine. Since your public IP address (the one your ISP provides you) is likely not static, you need a way to update your DNS name if your IP address changes. DynDNS is the easiest way to do this.

In your specific setup, it sounds like you don't have access to your router or gateway, so it likely won't work. I second the ""get external hosting"" option."