Do you use a 2018 MacBook Pro? if so, WiFiSpoof is not compatible - as the ability has been crippled by Apple.

Otherwise, the change button only becomes active if you manually change the Address in the MAC address field.

The scrolling field is an advanced option, which allows you to spoof your address (using the randomize button) as the listed vendor. For example, perhaps you want your computer to still identify as an Apple device after spoofing - you would select one of the Apple Inc options.

The vendor list is sourced from https://www.ieee.org, and all networking devices are identifiable according to this list: https://en.wikipedia.org/wiki/Organizationally_unique_identifier.