Just to clarify on the original question: an IP address is basically just your unique identifying number on the internet. Sorta like how if you make a phone call, it probably means you are dialing from a phone that has its own 10 digit number of some kind.
Your IP address itself does not reveal much more information about you than your general geographic location (such as your city). So when you go to websites or post on GT and your IP address is logged, it just tells them another (probably) unique visitor from your general area has visited their site.
I say "probably" because many IP's are considered "dynamic" in that your ISP assigns you a new one ever so often as one is free. Therefore if someone knows your IP address one day, it may be someone elses entirely the next day.
For someone to gain access to what websites you have been to, they'd need to get at the internet history stored on your computer, and they would need much more invasive access to your machine than just knowing your IP address gets them. You would likely have had to unwittingly installed a trojan of somekind for them to gain this. Or if you are using a company computer at your job, they may have installed tracking software to monitor your internet activity (which you can think of as basically like a company-run trojan)
While it's not exactly your full internet history, a website can know you are a repeat visitor if its placed a cookie on your machine that it sees when you return. This is likely not a security concern... but if it bothers you, you can disable cookies and clear them as desired. Although some nice features (like not having to login everytime you come to Glocktalk) are made possible because of a cookie.