The Congress is built up by the senate and H.O.R, each having their own responsibilities. The H.O.R. is based upon population because the people choose who they want. The politicians then are able to represent the people. The senate is based upon equality so that the states are equally represented.
The H.O.R initiates revenue bills. It also passes articles of impeachment.
The Senate approves presidential appointments like ambassadors, judges, and cabinet members. The senate also ratifies treaties.