Contains
  ->   one or more data files.
  ->   one or more control files.
  ->   two or more redo log files.
  ->   configuration file is very very important..that sets all parameters..
Database contains
  ->   multiple users/schemas
  ->   one or more rollback segments
  ->   one or more tablespaces
  ->   Data dictionary tables
  ->   User objects (table,indexes,views etc.,)
Server that access the database consists of
  ->   SGA  (Database  buffer,  Dictionary  Cache  Buffers,Redo log buffers, Shared SQL pool)
  ->   SMON (System MONito)
  ->   PMON (Process MONitor)
  ->   LGWR (LoG  Write)
  ->   DBWR (Data Base Write)
  ->   ARCH (ARCHiver)
  ->   CKPT  (Check Point)
  ->   RECO
  ->   Dispatcher
  ->   User Process with associated PGS

Distributed database is a network of databases managed by multiple database servers
that appears to a user as single logical database.The data of all databases in the
distributed database can be simultaneously accessed and modified.
This concept is useful companies spread over different locations..

ERASE  removes  an indicated Global variable & releases the
memory associated with it

SQL * DBA-> This allows DBA to monitor and control an Oracle database.
SQL * Loader-> It loads data from standard operating system files (Flat files) into Oracle database tables.
Export(EXP) and Import(imp) utilities-> allow you to move existing data in Oracle format to and from Oracle 
                                                              database.

DB  NAME  -  Must  set to a text string of no more than 8 characters and it will  be  stored inside the 
                        datafiles, redo log files and control files and control file while database creation.
DB_DOMAIN -It  is  string  that  specifies  the network domain where the database  is  created.  The  
                           global database name is identified by setting these parameters 
                           (DB_NAME & DB_DOMAIN)
CONTORL  FILES  - List of control filenames of the database.
                                    If name is not mentioned then default name will be used.
DB_BLOCK_BUFFERS  -  To  determine the no of buffers in the buffer cache in SGA.
PROCESSES  -  To determine number of operating system processes that can be connected  to  Oracle
                           concurrently.The  value  should  be  5 (background process) and additional 1 for each user.
ROLLBACK_SEGMENTS  -  List of rollback segments an Oracle instance acquires at database startup.

And Optionals - LICENSE_MAX_SESSIONS, LICENSE_SESSION_WARNING and
                           LICENSE_MAX_USERS.
 

The Default Table Space of a user is System Tablespace unless mentioned specfically while creating the user.

Monitoring of user access in the investigation of Database use.
Levels are Statement Auditing, Privilege Auditing and Object Auditing

Upto Oracle 9i Dropped table can not be restored.
But after that  in 10g the droppped table can be restored by using the Flashback command. 
*  syntax is ->  flashback   table    <tablename>  to  before  drop.

SYS_UNDOTBS and SYSTEM tablespace gets created automatically.

-> Temporary tablespace is locally managed tablespace  AND Permanent tablespace is dictionary managed tablespace
-> When an extent is allocated or freed for reuse changes occurs in tables.In case of Temporary tablespace changes happen in bitmaps but in Permanent tablespace System Tables gets updated.
-> Temporary Tablespace automatically tracks adjacent free space.