A subscriber pays a monthly fee and is able to choose titles accordingly per month. Every month your title is launched, you will get a share, regardless of subsequent launches, of the revenue. A launch is counted as ~20 seconds (subject to change) of runtime of a title by a user. This baseline time is to make sure a customer intentionally wanted to play a title.
Additional terms can be found here: https://developer.viveport.com/documents/viveport-subscription-service-terms.pdf