Coins are a currency in Bubblegum Simulator, mainly used to buy items in the Gum Store. By redeeming blown bubbles in the Sell Area, players get coins to spend to increase bubbles blown.
They are also scattered all throughout the map. They come in different sizes in the overworld - the number of gems you get is mutiplied by Pets and Gamepasses.
Coins are used to buy Gum and Flavors in the aformentioned Gum Shop. Low tier eggs - Common, Spotted, and Spikey Eggs are bought with coins as well. 5 Coins can be given to the Gem Genie to get 1 Gem.
All items/pets buyable with coins are shown below.