Article I of the Constitution gives Congress the power to do many things. The President must sign bills into law and can veto any bill Congress passes. The President can pardon a person impeached and removed from office by Congress. The Judicial Branch interprets laws passed by Congress and the Supreme Court, under it's power of judicial review, can declare laws unconstitutional, thus making them null and void. The United States Senate has 100 senators - two from each state.
Senators represent everyone in their state.
Oklahoma's two senators are Don Nickles and Jim Inhofe. Senators are elected to serve for six years, called a term. Senator Nickles was first elected in 1980 and was just re-elected in 1998 to serve his fourth term. The Senate is the only part of government that can approve treaties and nominations. The Constitution requires that a member of the U.S. Senate must be 30 years old, must have been a U.S. citizen for 9 years, and must be a resident of the state where they were elected.