go to the Sales → Customers → Edit Customer
Enhance the interaction with your registered Customers by adding a store credit or refunding Customers by store credit. After that, customers can use the store credit to make purchases on your store.
On customer's edit page can locate Transactions Tab. This page keeps all transactions history for the customer's account.
Customers can spend the credits earned. In the checkout, just click the "Apply" button
All transactions can be seen by customer in the My Account → Transactions section.