There are different ways of earning coins:
1) The easiest method of getting coins is daily bonus. Go to the app every day and get your reward.
2) If you watch advertisements you will get a reward.
3) One of the ways of getting coins is changing the collections.
4) When you complete quests you will get rewards (coins).
5) You can spin the Lucky Wheel every 2 hours.
6) You can buy coins in lobby or with special offers and packs (starter pack, full pack).
7) Another one of the easiest methods is a Piggy Bank.