Hi,
You need set enviroment variables to your .bashrc
Like below. It of course depend witch Oracle database you did install
Code:
ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
PATH=$PATH:$ORACLE_HOME/bin
export ORACLE_HOME
export ORACLE_SID=XE
export PATH
See this Oracle XE related document
https://help.ubuntu.com/community/Oracle10g