Basically a subscription renews itself at the end of each billing period (e.g. end of the month) for the next one automatically. The payments are automatic, so you don’t have to think about it.
Furthermore you can pause your subscription anytime (meaning the payment will be intermitted for a time agreed). Should you have a surplus of unused lessons, you can redeem your remaining credit anytime until it is used up.
The subscription can be cancelled anytime to the end of a billing period. After cancellation the remaining credit can be used until the last day of the billing period.