Paul,
1. you have to know the IP address your home network is known as on the internet. If it isn't static you need to set up one of the dynamic DNS providers to automatically map the IP to a name you know or you'll never know what the IP is.
2. you have to configure your router to forward traffic sent to a specified port on the internet side to whichever port the IP switch is listening.
eg Suppose your external IP was 241.202.202.202, (that looks valid but isn't) your internal network was 192.168.0.0/24 and the IP switch was 192.168.0.66 listening to port 80.
Pick an unused port number on the router - say 17000. Numbers between 16384 and 32767 are good choices. You configure the router to forward internet traffic sent to that port to 192.168.0.66 port 80.
Exactly how you do that depends on what brand and model of router you have.
From the internet you then
http://241.202.202.202:17000