How is the winner of the presidential election determined?

By the most votes by the people of the United States of America. Their votes

is tallied up for the next president.

That's a common misconception. The popular vote does not decide the president. A group of electors, the electoral college elect the president. The electors are senators and representatives from the House of Rep. While the electoral college using elects the same president as the popular vote the electors are allowed to vote freely. The founding fathers created the electoral college because citizens were poorly educated and it was feared that the people would elect a horrible leader.