A somewhat simplified explanation of the two houses forming the US Congress. From Quora.

The House and the Senate are the two houses of congress. They have fairly similar levels of power, in that they both have to pass a bill in order for it to become law (which is the chief power of congress).  The difference between them is that Representatives are based on population, each one intended to represent a specific group of citizens.  Originally, the plan was to have a Representative for every 30,000 Americans, but the population grew too big for that, so we’ve capped the number of Representatives at 435.  In any case, each state is divided into congressional districts, and your congressperson is supposed to represent you in the Federal government. They’re the one you’re supposed to go to if you have a problem with how the country is being run.
The Senate, on the other hand, is supposed to represent the interests of the states.  Each state gets two senators (no matter how big or small they are).  Originally, they were appointed by the state legislatures, but all states have gone over to voting for Senators directly.
The Senate was intended to be the more deliberative body, impacted less by the winds of politics and more given to in-depth examination (they serve six-year terms and have a tradition of unlimited debate).  The House was intended to be more vibrant, faster moving and closer to the people (they serve two-year terms and have strict limits on how long each member can speak).  The hope of this system was to strike a compromise between the dynamic populism of direct democracy and a more high-minded statesmanship.  At the same time, it was hoped to strike a compromise between the power of the big states (who have more representatives) and the small ones (who get the same Senate representation for a smaller population).
In practice, they don’t function that much differently.  Senators have to have statewide appeal, instead of appealing only to one districts, which means that colorful characters tend to be more common in the House.  The Senate is also uniquely able to block legislation because of the filibuster.  Other than that, they operate largely the same way.