Coins are a currency in Bubble Gum Simulator, mainly used to buy items in the Gum Store. You get Coins by selling your bubbles at any sell area. Coins are also scattered throughout the map. They come in different sizes in the overworld - the number of gems you get is multiplied by Pets, Hats, and Gamepasses.
Coins are used to buy Gum and Flavors in the aforementioned Gum Shop. Low tier eggs - Common (250), Spotted (3,250), and Spikey Eggs (35,000) 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.