I want to buy a graphics card ,I am little confused

You should list what use and expectations of the card are. With that current setup you will be limited before huge bottleneck occurs.

I need to play new games like fifa 13 ,pes 13 gta 4 etc

Have a look at the stickied thread, outlining how to ask for a new card, stuff like preffered sites etc helps make a recommendation, especially for people in other countries.

I dont understand anything

The main things people will need to know.
What you want to use it for, games, settings etc
What your current build is, including all components
Websites you want to buy the products from, as most people here will buy from american sites, and have US$ listed on them.