you can find your IP address by going to www.whatismyip.com
you can direct people to a personal webserver running on your machine by givnig them this IP address,
Yes, it's free, no you don't have to pay for it.
if you do plan to run your own personal webserver then I suggest you head off to somewhere like www.no-ip.com
where you can get a free address [subdomain].no-ip.com or sinillar for your computer, that will update if your IP address changes as well.