How to find and download free games and softwares for apple Iphone?

I have a apple Iphone. I have the USB connected to my Laptop. I also have the itunes installed in my computer. I would like to download some free applications and some racing games to my iphone. Do I need to sign up somewhere to use the itunes? Does the software and games available to download vary from country to country? Pls provide me the directions to enjoy the applications and the games.