Subject: Polity
In India's parliamentary system, the President is the ceremonial head of state while the Prime Minister is the head of government. As explained in Polity by Laxmikant, the President acts on the advice of the Prime Minister and the Cabinet, which means that the real executive power rests with the latter.
This relationship is governed by constitutional provisions (Articles 74 and 75), wherein the President is bound to act according to the advice tendered by the Prime Minister. In exceptional circumstances, however, the Prime Minister may need to justify the advice given to the President, thereby maintaining a system of checks and balances.
This symbiotic relationship ensures that while the President symbolizes the unity and integrity of the nation, the Prime Minister drives the actual governance and policy-making processes.