How can you win the popular vote and still lose the election with the Electoral College system?

In the US elections for President and Vice President, the Electoral College actually votes to determine the winner. Many states award their electoral votes "winner take all" so that a narrow victory is the same as an overwhelming one. If one candidate wins most of the very-populous states but not enough electoral votes, their large popular vote in those states does not do them any good.

The Electoral College was set up to avoid domination of the Presidency by candidates from the most populous states, at the expense of the more-numerous smaller states.