In case you don't already know, in the United States, the people don't vote directly for the POTUS, what we're actually doing is voting for electors, these electors will then meet in December at their respective state capitals, then cast a ballot for president. If candidate gets the most votes in a particular then he'll win that state's electors. Electoral votes are based on the populatin of state, California has the most (54, I think,) several states, such as Delware and Wyoming only have 3. The electors represent the state's congressional districts, plus their 2 sentors.
What sometimes is that a candidate will get more popular votes, but depending on the electoral votes of states he wins, can still loss the race.
Proponents of the Electoral College say it gives smaller states say in say in who will be president, Opponents say that the Electoral College circumvents the will of the people.