Coins are an in-app virtual currency that you earn through hitting savings goals and missions, playing the Daily Game, and more! You can use Coins to play games and enter the weekly drawing. You can also win coins from gameplay.
You earn Coins daily based on how much you are saving with Long Game: as your linked bank account balance increase, so does your daily coin rate, allowing you to play more games and win even more! Coins are also earned every time you achieve savings Missions.
You can see full earning rules here.