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.
When you watch a video from the appzone, and find a game Interesting are you supposed to earn some GS for it ? (That is if you do install it and play with it, like do you get x amount of SG per min/hour/day ...) Or only the 1 for watching the video ?