You pay to get the service for several period (hourly or monthly based rates).
Before its expiration, you can renew the service and get your expiration date extended.
Yes. Once you created a VPS, the resource needed (CPU, RAM, storage, IP address) is allocated for you regardless of the VPS power state, and therefore incur charges.
If you wish to no longer accumulate charges for a VPS, you have to destroy it.