In the subscription tab you will find the information about the customers subscription. If the subscription tab should be blank check the country settings of the account on the account detail page.
Next billing date: The next date when the account will be billed
Previous billing date: The last date when the account was billed
First billing date: The first date when the account was billed
Next monthly gross price: The monthly price of the subscription
Next monthly net price: The monthly price of the subscription that the customer will actually pay (can be reduced by vouchers)