Two Senators from each State for six Years, and a House of Representatives fixed by law at no more than 435 voting members
Background
The Congress of the United States is the legislative branch and has two chambers, the Senate and the House of Representatives; the first Article of the Constitution establishes their structure and powers.
The Senate clause as drafted reads: "The Senate of the United States shall be composed of two Senators from each State, chosen by the Legislature thereof, for six Years."
State legislatures continued to elect senators until adoption of the Seventeenth Amendment to the Constitution, which provided for popular election of senators, in 1913.
The Constitutional Convention approved two senators per state by unanimous vote, and adopted a six-year, three-class Senate so that one third of the members go out every second year.
A Senator must have attained the "Age of thirty Years" and have been "nine Years a Citizen of the United States", and must be an inhabitant of the State for which he shall be chosen.
"The Vice President of the United States shall be President of the Senate, but shall have no Vote unless they be equally divided"; the Senate also chooses a president pro tempore to preside in the Vice President's absence.
Treaties are made by and with the "Advice and Consent of the Senate", provided "two thirds of the Senators present concur"; the same advice and consent governs the appointment of Ambassadors, other public Ministers and Consuls, and Judges of the supreme Court.
In the House the number of voting representatives is fixed by law at no more than 435, proportionally representing the population of the 50 states, and each representative is elected to a two-year term; a representative must be at least 25 years old and a United States citizen for at least seven years.
Besides the voting members there are five delegates and a resident commissioner, who hold the same powers except that they may not vote when the House meets as the House of Representatives; the arrangement of a population-based House with an equal-state Senate is called The Great Compromise.
In plain words
The Great Compromise The Great Compromise — The agreement at the Constitutional Convention to represent citizens by district population in the House and by equal state shares in the Senate.
president pro tempore president pro tempore of the Senate — A senator chosen by the Senate to preside in the absence of the Vice President; the Latin phrase means president for a while.