He's not elected, he is selected by the Presidential candidate. When you vote, you are voting for a President/Vice President combination. However it didn't used to be this way.
http://en.wikipedia.org/wiki/Twelfth...s_Constitution
Basically, it used to be that you could vote for two people. The person with the most votes because President and the person with the next highest number of votes became VP. But they changed that (see 12th amendment) after it caused a major mess in the electoral college in ~1796.