1. Turn on your iPhone and navigate to the screen with the "App Store" button
2. Click on "Categories" and go to "Games" down the list a little
3. From there, change your sorting options
4. Select the game you want to buy it and download it - you'll need an iTunes account
Enjoy great games like Rolando and SimCity - I guarantee they'll make for some great times while you're waiting in line or riding the bus - never suffer through a dull moment with your iPhone ever again.