Hi Janaka,
You should have been prompted to enter username and password while installing BO.
You should use the same credential here.
Search more on CMS.
The CMS is responsible for maintaining a database of information about your
BusinessObjects Enterprise system, which other components can access as
required. The data stored by the CMS includes information about users and
groups, security levels, BusinessObjects Enterprise content, and servers.
Please refer to the link below for more information:
http://help.sap.com/businessobject/product_guides/boexir2/en/xir2_bip_admin_en.pdf
Regards,
Ashvin