well usually you find a http client, install it onto your system, configure the httpd, put your content on the box, check your internal ip (you can do this through console) ipconfig (windows) or /sbin/ifconfig (linux) or just ifconfig (if you're under root)
This will tell you your gateway (your router's ip address) and your ip address of the computer, remember them.
Login to your router, usually you can do this through your browser by going to http://[gateway
ip address here] looks something like http://192.168.0.1
something like that (for home networks at least). There should be port forwarding, Enable it for the ip of your server. Enable the correct ports also 80 for default.
You can sometimes subscribe to static ip service from your isp and purchase a domain name which points to your IP. If you decide not to do this you can still have people connect to you, just give them your external IP. It can be found at http://ipchicken.com