what is a new features of Dataguard in 12c

You might want to start here:  Database New Features Guide - Contents

This section talks about just DG new features: Oracle Database 12c Release 1 (12.1.0.1) New Features

Keep in mind that "12c" is not a version number. Its just a label. The document I linked contains info on 12.1.0.1 and 12.1.0.2 but you may also be talking about 12.2.0.1 which is in a different book.

Cheers,
Brian