For the giveaway you need to be logged in and scroll down on the GOG Homepage, to find the giveaway banner to claim your copy of the game. It's a bit like A Short Hike, that sort of zen experience but with you doing little mini quests to help rebuild a park. You can claim the game for free before it expires on Monday, at 2PM UTC.
Some lists they have you can look over:
Some good deals they have on popular games:
- Horizon Zero Dawn™ Complete Edition (-67%)
- Frostpunk: Game of the Year Edition (-72%)
- Pathfinder: Wrath of the Righteous - Mythic Edition (-70%)
- Warhammer: Chaosbane (-80%)
- Outlast (-85%)
- Project Hospital (-50%)
- Hollow Knight (-50%)
- ELEX II (-50%)
- RimWorld (-20%)
- Heroes of Might and Magic® franchise (-75%).
If you need help managing games on GOG I can easily recommend the likes of Heroic Games Launcher which supports Native Linux games and can manage the Windows compatibility layer Wine to play a ton more on Linux too, so you don't have to miss out on some great titles.