The USA is a presidential republic. The legislative power is vested in the Congress. It consists of the two chambers- the Senate & the House of Representatives. The Senate is made up of 100 members(2 from each state) elected for a term of 4 years. To be a senator, a person must be at least 30 & have been a citizen of the USA for at least 9 years. The number of Representatives depends on the population of the state. To be a Representative a person must be at least 25 & have been a citizen of the USA for at least 7 years. The head of the Senate is the Vice-President of the USA. The head of the House of Representatives is the speaker elected by the House. This branch prepares, considers & makes laws.
The executive branch consists of the President, The Vice-President & the Cabinet.. The Presidents term is 4 years. He is the head of the executive branch, he appoints the members of the Cabinet. The Cabinet advises the President oh many matters & is composed of the heads of ten executive departments : Secretary of State, Secretary of Treasury, Secretary of Defense & others.
The judicial branch is headed by the Supreme Court which settles disputes between the states. It may veto any law passed by the Congress if it contradicts the Constitution of the USA. The USA is a federal union, & the President is the head of the federal government.