The first time you insert a YubiKey, the Keyboard Setup Assistant may open. If it does, simply close it by clicking the red circle. For more information on why this happens, please see The YubiKey as a Keyboard.
Using your YubiKey to Secure Your Online Accounts
For registering and using your YubiKey with your online accounts, please see our Getting Started page. In many cases, it is not necessary to configure your YubiKey before using it with online services, so it is recommended that you make a configuration change to your key only if instructed to do so by setup instructions for a particular service.
Securing Your Local Mac Account with a YubiKey
For using your YubiKey to securely log in to your Mac, please follow the instructions in the guide Using Your YubiKey as a Smart Card in macOS.