Yearly vs Monthly Subscription
You can pay on a monthly basis. You will be billed each month (per user/per seat) and can cancel anytime.
Yearly billing provides you with a discount compared to the monthly subscription.
You can cancel your subscription in Settings > Subscription. This will stop the auto-renewal of your payment plan. The cancellation is immediate but if you are on a yearly subscription, you will have access to the app until the end date (next renewal date).