The three branches of the US government are the executive, legislative and judicial branches. They have co-equal powers within the government in a checks-and-balances system designed to prevent tyranny from occurring in any one branch of government. Each system can work autonomously using the powers vested in them by the Constitution, but they each operate in a way to control and limit the power any one branch can exert on the public.
The Executive Branch consists of the president and the cabinet departments. The branch has most of its power vested in the president of the United States. He is the head of the nation and holds great power to appoint cabinet members, ambassadors, and influence the strategic trajectory of the nation's domestic and foreign policy. The president maintains important checks on each other branch. The president can veto, or deny, the passage of a law by Congress, thereby limiting its power. The president also appoints justices to the Supreme Court, controlling the makeup of the court for future court cases. The makeup of the court is important because biases (conservative or liberal) can influence how they interpret the Constitution.
The legislative branch's power is vested in Congress. Congress is a bicameral legislature, meaning it is divided into two equal parts: the Senate and the House of Representatives. Congress has the responsibility to pass a law, control budgets, wage war and represent the people from their respective voting precincts. Congress controls the executive branch by voting on the presidential nominations for important offices.
The judicial branch is headed by the US Supreme Court. The Supreme Court is the ruling court of the land and has the authority to decide cases of national importance. There are many inferior courts, such as Courts of Appeal, Circuit Courts and state courts. The judicial branch can declare a law unconstitutional, limiting Congress's power, and can deny an executive action to limit the president.