Hello Everyone I Just want to know Could Anyone can tell me that how can buy a new free game on Gog.com anyone has knowledge about it.

I'm not sure if this is spam or not. What game did you want to buy? You go to the game page, click "Add to cart", click the cart icon (with a green "1" or other number on it) in the top-right corner, click "Go to checkout", select the appropriate payment options and info, and finally click "Play for your order now"

If you want to check out the free games here, there's a small selection you can browse: https://www.gog.com/games?page=1&sort=popularity&price=free (includes demos and some other things)

I'm sure.