The whole country is broken into tiny geographical regions called "ridings". I think each riding has approximately the same population, so those with lower population density are much larger than others. Political parties have representatives in each riding, if they are able to recruit enough people that is. Representatives names appear on the ballot. As voters we put an 'X' beside the name of the person representing the party we prefer. If a party cannot recruit a representative for a riding, then people in that riding cannot vote for them. For example, I doubt the communist party has a representative in my riding, so I couldn't vote for them even if I wanted to, which I don't.

When the polls close votes are counted within a given riding. The person that wins a majority gets a seat in parliament, regardless of which party he represents. Parliament is therefore filled with one representative from each riding across the country. The party with the most representatives is the one that governs. The 'opposition' are the party or parties that have fewer representatives. They will debate the pros and cons of each proposal that is presented to them.

The party leader is elected by party members before an election is even announced to the public. He is also a representative of a riding, and has to win a majority there. I'm not 100-percent certain (since I don't study politics closely) if he gets to be Prime Minister if he loses the election in his home riding. Not sure. Maybe not. My understanding is that he's usually a pretty popular guy all around. I might think the current Prime Minister is swell, but that doesn't mean I agree with the party platform. I understand that I am voting for a party platform, not a Prime Minister. If his party wins the largest number of ridings, only then does he become Prime Minister.

In short, we don't elect a Prime Minister, his name doesn't appear on the ballot unless he represents the riding you live in. We elect representatives, called ministers to parliament, or MPs. They represent their ridings. The Prime Minister has the extra duty as spokesman for the party. Other MPs might be appointed after the election for important duties as Minister of Finance, Minister of Energy & Environment, Minister of Defence, and so on...