what is Indian Audit & accounts?

The Indian Audit and Accounts service is under the Control of the CAG. The Controller and Auditor General of India (CAG) is one of the Constitutional authorities, like the Chairman of UPSC or the Election Commissioner. He/she is responsible for maintenance of accounts in the states as well as Audit of Accounts of the Union as well as the State Governments. The post of Controller and Auditor General is not, reserved exclusively for officers of the IA&AS. Even officer of the IAS of sufficient experience and seniority may be appointed as the Controller and Auditor General.

The services of officers of the IAAS are lent to State Government for functioning as Financial Advisers Chief Accounts Officers, Chief Internal Audit Officers and so on.
The hierarchy:
During the course of their probation, direct recruits to this service work as Assistant Accountant General. The heirarchy after that is: Deputy Accountant General 
   > Senior Deputy Accountant General 
       > Accountant General
          > Director of Audits 
             > Additional CAG 
                 > Dy. CAG (equivalent in rank to a secretary to the Government of India).