Hi, I have LG 47" LW4500. My display card is AMD Radeon 6900 series. What should I do next to enjoy 3d gaming?

You need a 3D driver. I would recommend getting the DDD TriDef driver, though the IZ3D should also work.

Thank you very much Cyberreality. Your advice was very helpful. I tried both of DDD tridef 3d and iz3d. I preferred DDD tridef because It's easier to setup and the image quality is better. Currently I'm playing L.A Noir. This game is not supported by niether software. Is there a way I can enjoy this game in 3d?

I haven't tried that specific game, but some of the time you can get the games to work even though they are not officially supported. If it just won't work at all, then you might have to wait for the driver developers to release a patch or profile for the game. With DDD someones there are community profiles, so check their forums. With iz3d you need to wait for them to release a new version, and they have been slow with updates lately.

As cyberreality has pointed out, someone here seems to have got it working MTBS LA NOIRE. Do regularly check GameGrade 3D database for regular updates on the games supported by the various drivers.