@kalaicompforensic, you might have to understand differences between Add On and Apps.
Splunk follows Common Information Model (CIM) for normalization of data for ease in correlation and reusability of data across various systems/apps. Documentation on CIM: http://docs.splunk.com/Documentation/CIM/latest/User/Overview
Splunk Add On ensures data ingested to Splunk is normalized and also a lot of other other performance, re-usability and correlation related features like Data Models, Saved Searches, Pre-built Panels etc to be used across specific and/or several Apps (when built upon CIM).
Splunk Apps are more User/Developer facing interface built upon such Add On which caters to specific Business needs/use case. Add On is not always necessary for Apps to function but CIM compliant Add On ensure faster/better App development and re-usability. Read about App and Add-On https://docs.splunk.com/Documentation/Splunk/latest/Admin/Whatsanapp.
In case of Splunk Add-on for ServiceNow and Splunk App for ServiceNow as the documentation for Add-on mentions, the same Add-on for ServiceNow will ensure that Knowledge Objects created can be reused across Splunk's premium apps as well like Splunk App for Enterprise Security (besides the Splunk App for ServiceNow). Details on using Add-on and App for ServiceNow including the installation is documented on Splunk Docs. http://docs.splunk.com/Documentation/AddOns/released/ServiceNow/About and http://docs.splunk.com/Documentation/ServiceNow respectively.
Since these are Splunk Built and Certified. You can get assistance for issues with these from Splunk using your Splunk Entitlement. Obviously, the Splunk Answers Community can also assist with any hiccups you face while using these or any other issues with Splunk. Hope this helps!
@garethatiag, thanks I did. I was waiting for others to pitch in if they felt something else needed to be added or other way of explaining the difference.
Thanks, we can always have multiple answers to the same topic but I have generally noticed that once there is 1 valid answer it's much less likely that someone will feel the need to post another answer...(unless they want to clarify the answer or similar).