Constitutional framework and position of Prime Minister.......

The Constitution envisages a scheme of affairs in which the President of India is the head of the executive in terms of Article 53 with office of the Prime Minister as heading the Council of Ministers to assist and advise the President in the discharge of the executive power. To quote, Article 53 and 74 provide as under;

The executive powers of the Union shall be vested in the President and shall be exercised either directly or through subordinate officers, in accordance with the Constitution.
— Article 53(1), Constitution of India
There shall be a Council of Ministers with the Prime Minister at the head to aid and advise the President who shall, in the exercise of his functions, act in accordance with such advice.
— Article 74(1), Constitution of India
like most parliamentary democracies the Head of State's duties are only ceremonial, the Prime Minister of India is the head of government and has the responsibility for executive power. With India following a parliamentary system of government the Prime Minister is generally the leader of a party (or coalition of parties) that has a majority in the Lok Sabha, the lower house of the Parliament of India. The Prime Minister either has to be a current member of one of the houses of Parliament, or be elected within six months of being appointed.