This tutorial supports the original ActivityBot Robot Kit (#32500) and the ActivityBot 360° Robot Kit (#32600). What's the difference?
This kit has HIgh Speed Continous Rotation Servos + External Encoders. The servo has a white-red-black 3-wire cable.
Look for instructions mentioning "external encoders."
This kit as Parallax Feedback 360° High Speed Servos. This servo has a white-red-black 3-wire cable, and a separate yellow wire for sending feedback signals. It does not use external encoders, as these servos have encoder sensors built right inside the case.
Look for instructions mentioning "Feedback 360° servos."
You will use these pieces during the hardware assembly.
These pieces won't be needed for the hardware assembly, so you can set them aside and save them for later activities.