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 played BDO for about 4 years. There is always a lot of options on what to do. Grinding is not necessary. Last time I did it was for some events year ago.