Coins are earned when customers give you tips in game levels. At the end of a level, you can see how many coins you earned in that level (sometimes there are extra coins rewarded for getting two or three stars in a level!). All coins earned go directly into your bank after the level is finished. Coins can also be purchased directly with Dinero.
Coins can be used to purchase upgrades for your restaurant. Each restaurant has a store where you can purchase upgrades that will help you to keep customers happy and serve them more quickly. Upgrades must be purchased separately for each restaurant, but they're well worth the investment!