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.
I have been watching a lot of videos in app zone to earn the SG. Now it is showing that to earn SG you need to do some other task ? I have waited a day to watch the videos and dont think its the daily limit issue.