The candidate who wins the popular vote in each state typically wins all of that state's electoral votes. However, there have been a few instances in which the winner of the popular vote did not win the Electoral College, and thus did not become president. This has occurred when the winning candidate won a narrow popular vote margin in several key states, but lost those states' electoral votes.
The Electoral College system was created in the late 18th century as a compromise between those who wanted the president to be elected by the popular vote and those who wanted the president to be elected by Congress. The Electoral College was designed to ensure that the president would be elected by a broad coalition of states, rather than by a small number of large states.
The Electoral College has been criticized by some for being undemocratic, since it is possible for a candidate to win the presidency without winning the popular vote. However, the Electoral College has also been praised for its role in ensuring the stability of the American political system.