The legislative branch of the United States, established in Article I of the Constitution, is composed primarily of the House of Representatives and the Senate. Together, they are the United States Congress.
The House of Representatives is composed of 435 representatives, and the number of representatives in each state is dependent on the population of the state, with heavily populated states allowed more seats in the House than those that are less populated. In contrast, the Senate is composed of two representatives, or Senators, from each state, resulting in 100 total seats in the Senate.
In addition to Congress, other legislative agencies that support Congress make up the rest of the judicial branch, including the Congressional Budget Office, the Copyright Office, and the Library of Congress.
Together, the legislative branch, among other duties and powers, are responsible for making laws, declaring war, regulating commerce, and determining taxing and spending policies. They also reserve the right to confirm or reject the majority of appointments (i.e., Cabinet members and Supreme Court Justices) that can be made by the president and have considerable investigative powers.
The process of lawmaking is a bit more complex, however. When a draft of a law—a bill—is proposed, it can be introduced to either the House or the Senate. A committee within this Congressional chamber then researches, questions, and edits this bill to bring to the floor of the chamber. Elected officials then propose additional changes and/or vote on the bill. If it passes, it heads to the floor of the second chamber of Congress. When both chambers finally approve a version of the bill that they can agree on, it is brought before the president, who can either sign it into law or send it back to Congress. If a bill does come back to Congress, however, it can still pass and become a law by a two-thirds vote from both the House and the Senate.