The biggest new feature in this build of macOS Sierra is the added support for Unicode 9.0 emoji. This follows the same update iOS received with iOS 10.2 that just got updated for public beta testers today. In addition, bug fixes and security improvements can be found throughout.
To install macOS Sierra 10.12.2 beta 2 on your registered Mac, head over to the “Updates” tab in the App Store and check for updates. There, you’ll find the new build ready to install. Just click the “Update” next to the macOS Sierra 10.12.2 Beta 2 listing and restart your Mac. The process may take a little while, so be patient and don’t turn off your Mac manually if you don’t have to.