Now, Let's see how it works for Customer.
As soon as Customer Registers into your online store,Credit points gets alloted for registration or subscribing newsletter (This will depend on customer activity, points will be credited if newsletter is subscribed while registration or after registration of customer or points will be credited only if admin have alloted points for subscription).
Now, Here Customer registered and subscribe to newsletter both, then $20 will be credited to his account, as alloted by admin for now.
Now, Customer can use the credit point from two places-
On shopping cart, or on checkout page like this-
Now, as soon as customer place the order, he/she will get notify via mail and changes will get reflected on Customer's store credit.
Here, used credit got deducted and new credit points $10(As set by admin) successfully alloted for placing order.
Note If Customer can use all credit points to pay for order total then Zero Checkout Payment method will get display on checkout page and shipping charges and tax charges may apply if applicable.