you must forward your port to the host computer. think of it like creating a pathway through your network.
for example. 'external ip:100' to 'internal ip:100' and tell HFS to listen on Port: 100
make sure your computer has a static internal ip address.
then use the Self Test with HFS to see if it is working.
later on you can apply for a dynamic dns service so you have a static address to give users. you will also need to configure an ip updating service, but first lets get access to the server