Not sure opening your PC as server is the right solution. Anyhow before that:
I assume you are using a router with NAT (Network Translation):
- Make sure you have a static IP and not a dynamic one. If you have a dynamic IP (your ISP will tell you), and it is most of the cases so, you will need to use some dynamic DNS setup like
http://www.noip.com/
- For the outside world, your PC will be seen as the IP of your router, so use something like:
http://www.whatismyip.com/ to know what is the IP people see
- On the router side, you must "wire" or configure a given port to your PC. Note that only 1 PC inside can offer a service on that port. So if you setup a web server (port 80), you can't offer 2 different servers. Anyhow, on the router configuration (and it depends on your router) you will have to specify a port and the PC which will offer the service for that port.
- On the PC, you will have to open the windows firewall to accept incoming connections on the given port.
All those basically are the same from 7 and 8, only the firewall configuration is a bit different but not overall too much.
I can't give you a detailed how to, because I have no clues what kind of router you use and it may even depend on your ISP.