I have a requirement where i have to fetch response from Call Back Url in salesforce. I am not sure how to create a Call Back Url and how to execute a class to parse the XML response. Basically I am integrating Right Signature with Salesforce. I need to update my record when Right Sign sends a response(XML) to the Call Back Url Thanks in advance!
You can create a public Force.com Site, and then give that Site Guest User Profile access to an Apex REST class to create a public Apex REST endpoint. That's the high level of how you'd do this, you can find details on that process over at developerforce.
Then, you'll want to study the Apex Developer's Guide to see how Apex REST can be implemented to accept POST calls, and you'll want to read the reference on XML parsing. It should be fairly straight forward once you have all the pieces.