Hi Manohar,
I would suggest to read some integration document.
This is not always you can connect with other system with webservice APIs, you have to check supporting scenarios in each system.
Connecting SAP and SAP Cloud could require middleware( SAP Process Integration or Hana on cloud).
In Your case first check SAP system, SAP Cloud connector or Gateway or other medium to integrate and also you have to find relevant BAPI.
Here is some linke which help you to understand Integration SAP and SAP cloud
1. SAP Business ByDesign – SAP Help Portal Page
2. http://help.sap.com/businessobject/product_guides/hci1/en/hci10_agent_en.pdf
And also watch videos in youtube SAP Hana Cloud Integration - SAP Customer OnDemand to on premise SAP CRM - YouTube
Hope this help, please let me know if you need more information
Thanks
Sunil