How can someone get my IP address?
Your IP address is generally obtainable under a variety of circumstances. Every computer you connect to on the internet will use your IP address to establish this connection and in most cases keep a log of your connection. While all servers and services will generally have access to your IP address, they usually do not share it with strangers across the internet.
Some software people use on a daily basis may be unknowingly sharing their IP address with total strangers. Applications that may be sharing your IP could be, applications for sharing files, messaging applications, and even some games. When using some of these applications they will directly connect users to increase connection speeds and functionality. While file sharing applications all share your IP between you and your remote connection, not all messaging applications or games will do this. Depending on the applications or games that you are using it may take some research to find other users may have access to your IP.
In the end it really boils down to every connection you make to use the internet involves your IP address. The good news is that even if someone gets your IP address there generally isn't anything they can do with it. In most cases someone can run an IP Address Lookup and narrow down which ISP you use and maybe which town you live in. Aside from that, unless they are a law enforcement agency with a warrant, you have have very little to worry about.