Note also : Tom Kyte on Oracle 12c
Tom Kyte on the Top 12 Features of 12c
Additional Resources :
1. Presentation on the 12c Architecture
2. Presentation on the Multitenant (CDB and PDBs) Architecture
3. Database 12c Interactive Quick Reference
Here's an "Awesome" List of Resources https://github.com/sindresorhus/awesome . . .