if you installed oracle client on sql server ,then what is the use of if.u need to create linked server to oracle client and then oracle client make connection to oracle server
If you do not install the Oracle client on your SQL server then the link connection will not work or not work properly.
When you create a "linked" connection in SQL server; the server itself is connecting to Oracle (or other SQL servers) and not your desktop.
To understand how linked server connection works I recommend Book On Line (BOL). In this article I am assuming that you know how linked servers work. It's not hard just takes some time to read through.
The only thing that the Oracle client is going to provide you is the correct drivers in order for SQL server to connect to Oracle.
I hope his answers your question.