The repository database stores all the information about connections, transformations, packages, SQL scripts, reports and execution logging. This is where the results of ETL designer hard work is stored and obviously, no one wants to lose it.
About
This article provides information about configuring Oracle Repository connection
To create new Oracle repository connection
Click Options
Click Plus
Enter a connection name
Set type to Oracle
Select/Enter TNS name or use instant client syntax
Enter username and password
Select database name
Make sure that connection actually works
To avoid problems always make sure that you are using the latest version of 32 or 64 bit Oracle client + OleDB Provider