The office of the president is also known as the executive branch. This 2018 History Channel video describes the powers of the president and how Congress and the Supreme Court keep those powers in check.
US Constitution
The powers of the president are laid out in Article II of the United States Constitution. The version below includes links to related amendments.
Chapter 2 Beliefs, Values and American Society Chapter 5 American Political Parties Chapter 6 Elections and Political Participation Chapter 10 The Presidency - Powers and Selection Chapter 11 The Presidency - Chief Executive