It appears that your problem is portforwarding.
Because your a novice, i assume your HFS is listening on port 80 (http default) on your computer: check in your browser 127.0.0.1:80 , you should get your HFS page.
Find out your LAN ip address, which is assigned to your pc by your router:
either find it in your router menu or enter in the DOS window "ipconfig /all". The "ip adres" probably starts with 10.0.0.x or 192.168.0.x , enter this ip in your browser and your hfs page should appear.
Enter the ip found in ipconfig /all at standardgateway in your browser: this will open the router config menu. Search for the the external internet address. This should be the ip you have given to your friend!
Search for the options NAT or NAPT or portforwarding and forward port 80.
Don't know how to do for your specific router, so read the manual or use the search. BTW There are many topics about this problem in this forum, search.
Ofcourse your fire wall should not block traffic on port 80 or block hfs, pls check or switch of temporarily.
Have fun.