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.
First of all, you cannot use a custom username in Wizard 101. This is a problem for multiple reasons, one being the fact that you need to have a similar username otherwise it doesn't work. Wizard 101 doesn't allow that. At all.