The House of Representatives & the Senate Form the U.S. Congress
So to summarize, there's,
The Congress: the bicameral legislature of the federal U.S. government, which is composed of two houses or chambers:
The House of Representatives: a popular chamber in which all states are represented proportional to their population (with at least one Representative); each representative serves for a two-year term. The house is presided by the "Speaker" who's is elected by the members.
The Senate: Also called the upper house (the lower house being the House of Representatives), each state is represented in it by two Senators for a total membership of 100. Senators serve six-year terms & there are elections every two years to renew the third of the seats.
The bicameral Congress arose from the desire of the Founders to create a House "of the people" that would represent public opinion, balanced by a more deliberative Senate which would represent the governments of the individual states, and would be less susceptible to variations of mass sentiment.