First, find out what the ipaddress is for the router.
Your Internet Service Provider will tell you this.
With KPN it simply 192.168.2.254 .
Login to your router.
Click on 'Access Control'.
Click on 'Port Forwarding'.
Add the rule service:[HTTP]'.Extrenal Host[*]'.
Internal Host[xx1.xx2.xx3.xx4]'.
You need to known your internal host ipaddress and it needs to be fixed.
Otherwise it will to work op a reboot and the internal host ipaddress changes.
Click the following button to set the internal host ipaddress fixed.
Protocol[TCP]'.
External Port[80]'.
Internal Port[80]'.
Chech whether the forwarding rule has been created.'.