What can anyone do with your IP address if they find it out?

I know I can find my own IP address out by going to various web sites. How can anyone find out mine though? And even if they did what can they do with it - if anything?

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia��).