Article II, Section 2 of the US Constitution states: 

[The President] shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the Supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments.

The President of the United States is vested with the considerable power to appoint thousands of different officials, ranging in power from low level regulators all the way to the Justices of the Supreme Court. This is an enormous task for one person to undertake, and the drafters of the Constitution provided for Senatorial advice and consent as a check on both abuse and poor performance in appointments by a President. 

The representatives each state gets varies by its population in the House of Representatives. So, California, which is currently the most populous state, gets a lot more representatives than Wyoming, which is currently the least populous state. In the Senate, every state gets two representatives, regardless of size. The system was set up this way because of a disagreement between state representatives at the Constitutional Convention. The larger states' representatives wanted to have their larger populations reflected by greater representation, whereas the smaller states' representatives feared they would have no power in the system and would be mere subjects of the larger states. A compromise was reached, which is called the Connecticut Compromise, or the Great Compromise.

In the American Legislature there are two houses. The House of Representatives, where each state is apportioned a different number of representatives relative to the population of the state, and the Senate. In the Senate, every State has exactly two members, regardless of the population of the state.

The House of Representatives is the lower house in the United States’ Legislative Branch. The American Legislative Branch operates as a bicameral legislature, with an upper house (The Senate) and a lower house (The House of Representatives).

The structure of Congress and the powers reserved for Congress are established in Article I of the Constitution.

The House of Representatives may bring charges of impeachment against a President, and if the vote carries, he is tried for impeachment in the Senate. Only two Presidents have ever had charges of impeachment brought against them by the House (Andrew Johnson and Bill Clinton), but neither were found guilty in the Senate.

Pork-barrel legislation is the name given by any attempt, successful or otherwise, by a representative to gain some benefit for his or her home district at the expense of national interests.