What does the executive branch do?

Article II of the United States Constitution establishes the executive branch as composed of a President and Vice-President, and as written in 1787 outlines the method of their election, terms of office, and duties. Among other things, the President is "Commander in Chief" of the military and has the power to make treaties, with the approval of Congress and the "advice and consent" of the Senate. The President in the same manner has the power to appoint justices of the Supreme Court (Article III of the Constitution) and various ministers (ambassadors) and cabinet secretaries. It is this last responsibility that gives rise to the vast scope of today's executive branch.
Initially, there were four cabinet departments: State, Treasury, War (now Defense), and Justice (the Attorney General). Today, there are fifteen cabinet departments. Each of these departments is a vast bureaucracy with thousands of employees, who regulate and administrate much of the government's affairs.
The executive branch shares power with the two other branches of government, Congress (Article I) and the Judiciary (Supreme Court, Article III). Throughout U.S. history this balance of power has shifted. During the Civil War, for example, the executive branch under President Lincoln had far greater power than the other two branches. After Lincoln's assassination and the end of the Civil War, Congress was the most powerful branch. In the last years of the twenty-first century through to today, the executive branch has generally been the most powerful. This is a result, in part, of the growing size of the federal bureaucracy; but further, it is the result of the President's expansive war powers. According to the U.S. Constitution, only Congress has the authority to declare war. Yet, in Article II, the President is designated as "Commander in Chief" of the U.S. military. As such, presidents since World War Two have used this role to conduct military actions, indeed wars, as an exercise of this role and without congressional approval.

The executive branch of the United States of America's government is charged with carrying out and enforcing federal laws.
The officials in charge of the executive branch of the federal government include the President, the Vice President, and the President's cabinet members (who are appointed by the President and must be confirmed by a majority vote in the Senate). There are fifteen executive departments, and they are the departments of:
agriculture
commerce
defense
education
energy
health and human services
homeland security
housing and urban development
justice
labor
state
interior
transportation
treasury
veterans affairs
As the head of the executive branch the President has the power to veto proposed laws, negotiate treaties with countries outside the U.S., appoint federal judges, and grant pardons; these powers are guaranteed by the U.S. Constitution. The President can also issue executive orders to bypass Congress, at least temporarily. Executive orders have included President Truman's integration of the armed forces and President Obama's increase of minimum wage for federally-contracted employees.