It really depends, to start you do buy a summoners spell book that gives a bunch of starting cards then daily quests can lead you to open a chest daily which will contain DEC, potions and/or monster cards and if lucky maybe a gold foil and/or legendary card which go for very high prices.  Just playing the game daily many players have made big money, I have the first link in the long line I provided in the post that says Nasdaq, this is a nasdaq writer than bought the $10 pack and sold 1 card for $2,700 dollars so typically you will make nothing playing free until card values go up and you accumulate some DEC yet in time with small investment into cards or rentals you can gain higher rank and get larger rewards hence making more the longer you are here.  Also you can stake the many Cryptocurrencies they have and earn SPS in airdrops from it.  Click my name and look at a couple posts I have shared about it, many sources proving they are growing fast and many are making good money.