What is the Medicare fee-for-service?

Excuse me, could you please clarify what the Medicare fee-for-service system entails? I'm curious to understand how it differs from other healthcare payment models and how it works in practice. Does it involve direct payments to healthcare providers for each service rendered to Medicare beneficiaries? If so, how are these fees determined and regulated to ensure fair pricing and quality care? Thank you for your time and assistance in explaining this topic.