Hi Harikrishna,
1. What is the difference between Node and Node Manager ?
A
Node Manager is a WebLogic Server utility that enables you to start, shut down, and restart Administration Server and Managed Server instances from a remote location.
Node now there is nothing like node in weblogic servers but many people refer managed servers as Nodes.
2. What is the difference between Admin server Vs managed server ?
A
Admin server can be only one for a Domain, which works like a Central Configuration/Monitoring controller for the entire domain
Managed server are similar to the Administration Servers, except few differences. Like Managed Servers will not have Administration Console Application (consoleapp) deployed in it
3. What is the relationship between Node/Node Manager to Admin/Managed Server ?
A Now Node Manager is needed to start/stop managed servers from the Admin consoles
To get more information on them check out the below link
Topic: WebLogic Initials
http://middlewaremagic.com/weblogic/?p=1914