hi
Yes you have to install Oracle client on BO server and since you are using IDT or Universe designer in BO server you have to install 32 bit Oracle client.
TNS entries are the service names that will be required to have communication between your Oracle client(on BO server) and Oracle server.
You can take help of your Oracle DBA to get the service name from Oracle server and use it on your tns file, which will be created once you install Oracle client on your BO server.
Thank you,
Haresh Pipariya