The Yubikey Token is an USB device that emits an event based One Time Password. You can initialize the Yubikey using the tool ykpersonalize. Paste the secret hex key here. For tokens compatible with the Yubico cloud service check "emit a public ID". When programming the token the prefix must be 6 bytes, which will give you a UID with 12 characters. You also need to choose, if the Yubikey emits the additional UID, which is either 12 or 16 characters long. You can check this in the test field.