How do I program my keyless entry remote in my Audi A4?

I recently bought a used Audi A4 and it did not come with the owner's manual. How do I program the keyless entry remote to unlock and lock my car?

First, ensure that your keyless entry remote is compatible with your Audi A4. Then, insert your key into the ignition and turn it to the 'On' position. Press and hold the 'Unlock' button on the remote for at least 10 seconds. Release the button and you should hear a beep indicating that it has been programmed.