I'm a bit unclear on what you mean so I'll offer a couple of possibilities.
If you mean you don't know how to get your domain to point to your website: just make sure that
www.yourdomain.com points to the public IP of your server.
If you mean that your server is behind a firewall and you don't know how to have it serve your web pages. Point
www.yourdomain.com to your routers public IP addess and have your router NAT the traffic on port 80/443 to your Debian LAMP box.
Hope this helps. If not, give us more info