The Constitution of the United States was the end product of the Constitutional Convention in Philadelphia, Pennsylvania. The convention was convened by the congress of the United States formed under the Articles of Confederation to form a more perfect union by amending the Articles of Confederation. Disobeying orders, and risking charges of treason, they instead designed a new constitution to replace the Articles of Confederation. This new constitution layed out a new and stronger government with its powers divided into three separate branches, and transformed the pure republic that was United States of America under the Articles of Confederation into the democratic-republic United States of America under the Constitution of the United States of America. These branches being named the Executive, Legislative, and the Judicial.
The Legislative branch, composed of Congress, is the main body of the United States government. Congress is divided into two houses: the Senate, and the House of Representatives (or the Upper and Lower Houses, respectively). The House of Representatives (often called "The House"), composed of popularly elected representatives, the number from each state being determined by the states population. The Senate, however, is composed of representatives, two from each state, regardless of population. Congress has all the power to create laws and policy within the confines of its constitutionality. Power of Impeachment is owned by the House, and the Senate owns the right to try Impeachment. Congress regulates all congressional elections; raises money through taxes, duties, imposts and excises; may borrow money on the credit of the US; regulate commerce with foreign Nations, States, and native Americans; to make and determine the value of money; determine the standards for weights and measures; establish the Post Office; protects copyrights and trademarks; create inferior courts; establish the crimes on the high seas; the punishments of offences against the laws of foreign Nations; power to declare war; maintain the military; organise, discipline, arm, and call out the militia; rules of the District of Columbia; and enact laws to enforce the Constitution.
The head of the Executive branch has the title of "President". The President being a natural born US citizen, civilian, and thirty-five or more years of age. The President is the Commander in Chief of the military. With the consent of the Senate, the President may appoint ambassadors and a number of other government officers. The Presidents final duties are: to occasionally inform Congress on the condition of the United States including his advice, for Congress's consideration, to preserve the good order of the United States; to meet with visiting foreign dignitaries; ensure the laws of the United States are faithfully executed; and commission all the Officers of the United States; and enact the laws and policies passed by Congress. Instead of enacting Congress's legislation, the President may veto it. However, Congress may override that veto and pass it without the President's consent.
The Judiciary branch has all the power to try, except in the case of Impeachment, and to inform Congress and the President of the constitutionality of legislation that Congress may be considering. If legislation is passed by Congress, and then further enacted by the President, but later determined to be unconstitutional by the Supreme Court (the head body of the Judiciary branch), the legislation can be made void. The Judiciary is not allowed to create nor enact laws.
The three branches breaks the overall power of the Federal Government so that no one person has all the power. Congress, as a whole body, has the most power, but that power is divided among Congress's several representatives of the Nation's Peoples. Further, Congress's power is put in check by the President, who is also put in check by Congress. Finally, both of these branches actions are put in check, based on the constitutionality of those actions, by the Supreme Court.