Reference article
Coins (Duck Life 8: Adventure)
Bronze, silver and gold coins share one spendable balance in Adventure.
Earning and spending
Find overworld pickups, collect coins during training, complete quests and win encounters. Shops spend the same balance; the gold/silver/bronze display is a denomination breakdown.
Other currencies
Jelly Coins and 
Arcade Tickets have separate uses and balances.
Across the games
Compare games and editions on the 
Coins page.