How does a cryptocurrency payment service work?

Could you elaborate on how a cryptocurrency payment service functions? I'm curious about the entire process from start to finish. For instance, how does a user initiate a payment? Are there any specific steps they need to follow? What happens once the payment is initiated? How is the transaction verified and processed? Are there any specific fees or charges associated with using such a service? Also, is the payment process secure and what measures are taken to ensure the safety of transactions? Understanding the intricacies of a cryptocurrency payment service would be immensely valuable.