National elections in Canada are conducted much like national elections in Great Britain. Voters in local ridings elect members to the House of Commons. The House of Commons then selects a Prime Minister from among its members.
Elections in each riding are conducted using a plurality system. There is only one member from each riding and whichever candidate gets a plurality of the vote (more of the vote than anyone else) wins. The members of the House of Commons then determine who will be the Prime Minister. The PM is generally the leader of whichever party can gain a majority of the seats in the House of Commons. He or she is not elected on a nationwide basis like the President of the US. Instead, the PM is simply a member of the House of Commons, elected by his or her riding, who is then selected as PM by the House.