Some of those free games come form the video card manufacturer. You register the card with the manufacturer and get the games.
Othertimes through Newegg you need to add the games to the cart as you order it. When you view the card, there is a link for the free games and you add them to the cart. It's a promo from NVidia.
For example right now Rise of the Tomb Raider is $0.99 if purchased with a 960 card. You jsut add it to the cart in Newegg.