Play games
Choose the game that interests you and play itfor free.
Complete the quests
Every game has some quests for which you will receive Soul Gems.
Receive rewards
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
Got an email from the developer saying they were changing their earlier key giveaway to a free to add instead for 72 hrs this weekend. https://store.steampowered.com/app/883680/Four_Kings_One_War/