You can use coins for purchasing new puzzle packs from the Puzzle shop. The price in coins is indicated on every paid pack.
You can also use coins to buy boosts which help you solve puzzles.
You can earn coins by solving puzzles and watching bonus videos. You can also ask your friends to send you coins by tapping on the plus sign next to the amount of coins choose "Ask friends". Please note that you and your friends should be logged in the app via Facebook.
This option is available only once a day.
The maximum amount of coins that one friend can send you is 10 coins or 1 energy point.
If you need more coins, you can purchase them in the shop - click on the plus sign next to the amount of coins.