How to drop database.

SQL> startup mount exclusive restrict;
ORACLE instance started.

Total System Global Area 1252663296 bytes
Fixed Size    2252824 bytes
Variable Size  788533224 bytes
Database Buffers  452984832 bytes
Redo Buffers    8892416 bytes
Database mounted.
SQL> drop database;

Database dropped.

Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options