Wie funktioniert eine Bitcoin-Zahlung?

How does a Bitcoin payment work, could you elaborate on the process in a concise manner? I'm particularly interested in understanding the steps involved from initiating the payment to its final confirmation on the blockchain. Does the transaction require any intermediaries or does it occur directly between the sender and receiver? Additionally, how secure is the payment process and what measures are taken to ensure the integrity of the transaction? Finally, how does the transaction fee work and how does it impact the speed and finality of the payment?