What can another person do with my IP Address?

[Joe]

They can't do any of those things. All they can really do is do an IP address look up which will only tell them what state you are in and city but the city is where your ISP is they could also contact your ISP and get a court order and find out where you live but that's only possible if there in law enforcement. I suppose if you they knew your IP address they could attempt to hack your computer but if your behind a router they can't do much of anything at all unless you have a service running on your computer that is publicly accessible (eg apache web server, OpenSSH, ftp, minecraft, SMTP, etc) and have opened the port on your router so the service can be accessed from the outside world. So I wouldn't worry if someone knowns you IP address and is trying to scare you.