The U.S. Constitution divides our Federal government into three separate but equal branches -- Legislative, Executive, and Judicial. This was designed to prevent abuse of power through a system of checks and balances, although some argue that the executive branch now dominates the other two.
The Legislative branch, or Congress, makes our laws. Congress is bi-cameral, meaning it has two chambers -- the Senate and the House of Representatives. One hundred Senators, two from each state, are elected by popular vote to serve an unlimited number of six-year terms. There are also 435 Representatives, the number from each state determined by its population. They serve two-year terms, although due to gerrymandering, fewer than 10% of all House seats are contested in each election cycle.
The Executive branch of government, administered by the President, is supposed to enforce the laws that Congress makes. The President is elected every four years when voters go to the polls and activate a process called the Electoral College where 538 electors vote for the winner. As we saw in November 2016, it is possible for a candidate to get the most popular votes and yet not win the electoral vote of the Electoral College.
The Judicial branch includes the Supreme Court, whose nine justices, appointed by the President, evaluate the constitutionality of laws. The federal judicial system also has lower courts located in each state to hear cases involving federal issues.