If your not already logged in, do so now and shutdown the database.
bash-2.05$ sqlplus /nolog
SQL*Plus: Release 10.1.0.2.0 - Production on Wed Oct 6 11:25:46 2004
Copyright (c) 1982, 2004, Oracle. All rights reserved.
SQL> connect sys/passwd as sysdba;
SQL> shutdown immediate;
ORACLE instance shut down.
There are a variety of different shutdown methods other than immediate. Using
shutdown without an argument is rarely used because the database won't shutdown
until all connections have been disconnected willingly, during which time it
simply won't allow any new connections. The problems is that if a session is
hung or a user went to lunch without disconnecting it could take a long long
time. Shutdown immediate will safely close out all current connections
regardless of whether or not they want to.