Article two of the Constitution of The United States discusses the Presidency. The President is the executive branch of The United States Government. He must be at least 35 years old and must be a natural born citizen. The President serves a four year term. The President is required to be compensated financially for his services.
Originally the President was the winner of the presidential race and the vice-president was the runner up. This was all changed by the 12th Amendment.
The Article also establishes the electoral college. The electoral college is the process of which the United States goes about electing their President and Vice-President. Each state has electoral college votes, the votes are the number of the states Representatives plus two senators. When a Presidential candidate wins a state they win all of the states electoral votes. The President must have 270 electoral votes in order to win the race.
The President has been given several requirements to fulfill by the Constitution. He is the Commander and Chief of the Military. He is also given the right "by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments." (Source)