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 dont know but i would like if there was more guns in CS:GO. Playing with same weapons gets boring after some time, i would like if there was weapon like scar just for diversity.