Reasons to create a database after installation are as follows: Database creation prepares several operating system files to work together as an Oracle Database.You only need to create a database once, regardless of how many data files it has or how many instances access it.
To greatly simplify this planning task, consider using Oracle Managed Files and Automatic Storage Management to create and manage the operating system files that comprise your database storage. All character data, including data in the data dictionary, is stored in the database character set.
You specify the database character set when you create the database.
See Develop a backup and recovery strategy to protect the database from failure.
It is important to protect the control file by multiplexing, to choose the appropriate backup mode, and to manage the online redo log and archived redo log files.
You typically create a database during Oracle Database software installation.