The U.S Congress was designed to be the legislative branch of the federal government. It has independent powers which are defined by the U.S Constitution and it's main responsability is to make the country's laws.
Moreover, it is separated from the executive and judicial branches of the government and it has two houses: the Senate (which is represented by only two senators) and the House of Representatives (which has representatives of their states/districts). Those representatives vote on behalf of all the citizens and the country's best interests.