Oracle Database 12c R1 (12.1.0.1) is now available to download from OTN and documentation is available here
From installation point of view 12c database is similar to 11g database with exception of Container Database (to support Multi-Tenancy and Virtualisation). More on Multi-Tenancy Architecture in Oracle 12C database (or Support for Virtualisation) here , here , here and later (in my upcoming post about PDB & CDB i.e. Pluggable Database & Container Database )