You first set up a passkey for a supported website on one Apple device, such as an iPhone. With iCloud Keychain, that passkey is synced across any other Apple device you own, such as an iPad or Mac.

However, it's important to note that not all iPads can be set up as a Shared iPad. Only those with at least 32GB of storage and running iPadOS can be used for this purpose; fortunately, it's easy ...