The purpose of this Forum Section is to trade for items in-game. Between members who have the game and want to trade in-game items.
This Forum Section is not for trading for items that have real world value, which include money or the game itself.
Not sure what your friends told you, but there isn't a specific place on these Forums where members will give away the game. Occasionally. members will do giveaways of games, which include for Terraria. However, it cannot be predicted when it occurs. It will be up to members to watch for givaways such as this on their own.
The game frequently goes on sale overall. Sometimes being as low as $2.50. Unfortunately, it will be hard to find people who will be willing to buy the game again to give it away unless you know them well. Announcements appear on this site when the game does go on sale. My best advice is to watch for those announcements.
This Thread is locked for the reasoning I wrote.