You buy Steam games you think people will like as gifts with your gift cards. Then the gifts will be in your Steam inventory. Then you go to the latest classifieds thread here and create a post. In this post, list all the Steam games you have for trading and list all the GOGs you want. People will private message you if they want to trade with you. You can also private message people if you see that they have GOGs you want. If a deal is made, add them to your Steam friend's list and then send him or her, the Steam game(gift). Do this before or after you get the GOG code from the person. Make sure you only trade with people who have a good reputation so you don't get scammed.

thanks for info.

No problem.

Just be sure to buy them as gifts. Otherwise you won't be able to give them to other people.

i will thanks for the help everyone.