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 haven't bothered to sign up to VIP because having a look at the potential benefits, it is well not worth it. To start, $4USD is roughly $6.60AUD. Cost of membership to VIP benefit is not equal amongst different countries. I understand it is easiest to earn money in one currency, but that also means that some are paying more money for equal benefits. Secondly... the available VIP exclusive chest have a 5 soul gem reward... if I'm going to give you money to be exclusively rewarded, I want a guaranteed 50 soul gem minimum. The new minimum for non-VIP members is 1 soul gem. Changing the minimum for non-VIP members is a pretty giant middle finger, particularly to those that have been using the site for quite some time. At the end of the day, it comes down to what you're comfortable with. You do get more than a non-VIP member.