IIRC it means you can install the Play Store instead of just having Amazon's terrible Fire store.
It's just grey-scale colors.
Completely different from Fire Amazon tablets.
The only thing I remember about jailbreaking, was being able to use custom screensavers and fonts.
Instructions are on the android Police website. https://www.androidpolice.com/install-play-store-amazon-fire...
The Play Store is a great improvement, it has far more apps and newer versions than the Amazon app store.