Here, you can find some info on the coin system of the Xeropan app.
Inside the application there is a coin system at work, you can buy the learning content through Xeropan coins:
1 coin = 14¢ (American cents)
You can purchase the coins in packages. You can read more on that here: What are the costs of using Xeropan?, or you can earn free coins as well. See the following article for more info: How can I earn free coins?