Explain how the seats in the house of representatives are picked? . what plan is that?

Each state elects two senators, while seats in the House of Representatives are apportioned by state according to population, with each state receiving a minimum of one representative.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.