What happens when you send bitcoin to someone?

As a keen observer of cryptocurrency and finance, I'm curious to understand the mechanics behind bitcoin transactions. Could you elaborate on what exactly happens when someone decides to send bitcoin to another individual? I'm particularly interested in the process from initiation to confirmation, including any steps involving mining, transaction fees, and security measures. Additionally, I'd like to know if the transaction is irreversible once it's been sent and how long it typically takes for the receiver to access the funds.