After i install oracle client 11.2 like this in Ubuntu 12.10 32-bit Machine
alien -i oracle-instantclient-basic*.rpm
alien -i oracle-instantclient-sqlplus*.rpm
alien -i oracle-instantclient-devel*.rpm
and start sqlplus
It ask for username & password, what is the username & password ...?
If you started sqlplus without any arguments, it would be a username and password for a database on the same machine, which is probably not what you want.
You should read up on how to use sqlplus: http://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_three.htm
Ask your database administrator for the correct database, username and password.