Hi Swathi,
Check these links:
CREATE using CRM_ORDER_MAINTAIN simple example (for those new to CRM and/or ABAP)
UPDATE using CRM_ORDER_MAINTAIN simple example (for those new to CRM and/or ABAP)
Creating and changing transactions using BAPI’s in CRM | SAP CRM by Gert-Jan Stolmeijer
Please, mark as correct if helps.