Congress is made up of two houses: the Senate and the House of Representatives. Encyclopedia Brittanica notes that the House is the larger legislative body; its membership number is determined by the population of the states. The Senate is the smaller, but more revered, chamber. Every state has two senators.
The House of Representative is considered the lower house of Congress. It was created to represent the people of the United States. At the Constitutional Convention, the creation of the House of Representatives satisfied the states with large populations, who benefited from proportional representation. Members of the House of Representatives serve two-year terms. The House is meant to respond to the needs and attitudes of the people, and react decisively to the exigencies of the moment. Because the House is seen as the voice of the people, it is the only body empowered to originate bills imposing taxes.
The Senate is considered the upper house of Congress. At the Constitutional Convention, its creation satisfied the smaller states, which benefited from equal representation. Senators serve six-year terms. This makes them less responsive to the momentary whims of the public. The Senate is meant to temper the impassioned, precipitous nature of the House. The Senate approves presidential appointments of federal judges, ambassadors, heads of federal agencies and cabinet-level positions.