There are actually some subtle differences here.
A Member of Congress is literally your representative. Members of Congress are elected by geographically regional districts in proportion to the population of those districts, and are intended to literally be the voice of the people who elected them. At the time the constitution was being drafted, the 'model' for the House of Representatives was the British House of Commons.
By contrast, the Senate was intended to be a place where serious, thoughtful debate took place, and the framers of the Constitution thought that the way to achieve that was to separate the concept of 'representation' from Senate membership. That is, Senators were intended to bring independent, impartial wisdom to the role and not necessarily directly represent the population of their states. So they came up with the idea that each state would be allowed two Senators irrespective of population. The idea behind the Senate was originally to emulate the British House of Lords, but with the notable exception that the writers of the Constitution wanted to avoid at all cost the notion that membership in the 'upper house' would be something that would be passed along to the actual family heirs of the members. To achieve that, the original concept was for Senators to be appointed by the Governors of the states, but experience led to the conclusion that the appointment process was an opportunity for political mischief. So the Constitution was amended to provide for election of Senators, but still with each state still having only two Senators.
So, the theory is that members of Congress are elected, and re-elected to represent the will of the people (and the term of office is only two years so that the election can reflect changes in public opinion), but your Senator are elected for their impartial wisdom and not on the basis of how well they represent your wishes. And to help separate popular whim from the electoral process, Senators have six year terms.
That's the theory. What happens in practice may be something entirely different.
