There are different ways that a country can organize a legislative branch. Specifically, the U.S. Congress is composed of two separate bodies, the House of Representatives and the Senate.
The House is made up of representatives that are elected every two years. The number of representatives each state is allocated is proportional to population based on most recent census data. There are 435 representatives in the House. The Senate has only 100 senators. They are elected for periods of six years, and there are two for each of the 50 states. Laws and other bills, including the budget, must pass through both bodies of the U.S. Congress before moving on to the president to be enacted into law.