If you can find out the IP address of an Internet user, you can get a rough idea what part of the country or world they're in by using an IP Lookup tool.
You should only be able to find out general details about them and NOT, for example their name and exact address. However, any IP lookup will give some or all of the following:
The ISP that is being used and organization's name
The IP's host name
The country it's in
The city (although this is often only accurate to 10 miles or less)
The latitude and longitude of the location (again not exact)