Passkeys are a form of passwordless authentication. You store them in Bitwarden like regular passwords, but when you want to access a site that supports them (e.g. eBay) instead of asking for you password and autofilling or copy pasting it from Bitwarden your Bitwarden pops up and asks you if you want to login and it just happens (if you have multiple passkeys associated with a site you can select which you want to use). That’s it. No password fields which get autofilled and no password in your clipboard (history).