Passkeys are an emerging technology aimed at replacing traditional knowledge-based authentication methods like usernames and passwords by utilizing cryptographic key pairs, enhancing security and user-friendliness. This guide provides detailed instructions on enabling, managing, sharing, and deleting passkeys across major platforms such as Apple, Google, and Microsoft, highlighting the differences in their implementation on various devices and operating systems. Apple users can manage passkeys via the Apple Passwords app on macOS and iOS, while Google's Chrome browser uses Google Password Manager for passkey storage and synchronization across devices. Microsoft employs Windows Hello for passkey management on Windows 11. The guide emphasizes best practices for passkey management, including enabling cloud synchronization, regularly reviewing stored passkeys, setting up recovery methods, keeping devices updated, and considering cross-platform compatibility. This shift towards passkey adoption is advancing interoperability and ease of use across different digital ecosystems.