I am new to the Mac and don't know how to use it correctly. When I surf the net, and I type in a web address, some of the old addresses appear in what was typed before. My problem is, how do I clear this?

I do find it helpful, but sometimes, I find it a nuisance in, it comes up what I don't want. I tried clearing the history and what not, but when I still type in a URL, the old stuff, still shows up. How do I clear this?