Installing oracle_10g Express edition in ubunto12.04 manually

[Priya chek]

Hi,
Iam nor able to install oracle_10 g express edtion in my ubunto 12.04. when i try to install after getting the key & after installing update getting error like

sudo apt-get install oracle-xe

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package oracle-xe


please help me install..plzzz