Prathik,
Querying and EntitySet is not the right way to get an operation done. Instead you need to use Function Import. Querying an EntitySet is expected to return entity instances. (entries).
I would suggest you to go through Gateway Documentation and understand the OData model and Operations before going further. (You may start with self paced learning at http://wiki.sdn.sap.com/wiki/pages/viewpage.action?pageId=318672261 )
Thanks
Krishna