For what its worth, I never really knew what a primary was either until just a couple years ago. They never taught anything about it in school.
So yes, the education system does fail often when it comes to teaching politics.
Anyway, to answer the author's question, primaries are held with the purpose of selecting the candidate who will become the party's nominee.
In this election year, we had 10 democratic candidates for president, and on the republican side, we have President Bush. He's the incumbent...or sitting president, and is not being challenged for the nomination by any other republican. So, on the republican side, he is running unopposed.
The primaries give the candidates a chance to get their message out to the people. Then, based on how their message appeals to the public, how hard they campaign, and how their character comes across, the voters will choose the candidate of their choice.
Any candidate that receives 15% or more of the popular vote in a state primary, will receive some delegates. Delegates will be divided amongst the candidates based on how much of the popular vote they have captured. Each state has a certain number of delegates up for grabs. Candidates need to win a good amount of the vote to win these delegates. When the Democratic National Convention in Boston comes around, the candidate who has the most delegates will become the Democratic Presidential Nominee. There is a minimum of 2,161 delegates required to receive the nomination, and a majority.
Once the nominee is selected based on who has won the most delegates, he or she can now pick the Vice President of their choice. Usually the vice president is selected by the nominee based on number of delegates captured, public appeal, and strength that he or she can add to the ticket. The goal after all is winning enough votes to become president in the general election, and having a vice president who may appeal to groups that the nominee does not...can help increase the chances of winning for the nominee.
Now that the nominee, and the vice president, are selected, they will run against the incumbent president (in this instance).
Because the nominee and the vice president likely have already campaigned in most of the 50 states, they have already established some of their voter base for the general election, as its likely those who voted in the primaries and caucuses will vote for the nominee of the party. The important thing now for the nominee to do is win the votes of the undecided voters, independents, and yes, some voters from the opposing party too. So now the campaign shifts gears from trying to appeal to the primary voters in each state...to trying to appeal to the voters of the nation as a whole. No easy task.
By November, campaigning ends and the general election occurs, and the voters of the nation vote for their presidential candidate.
I'm going to assume here that since you didnt know what the point of a primary was, you probably don't know how the electoral system works either. I didn't for a long time. Here's how it works:
The electoral system in presidential elections is only used during the general election and not during the primaries. Each state has a certain number of designated electoral votes based on the population of that state. For example, a rural state like Idaho only has 4 electoral votes, but a populous state like California has 55 electoral votes.
What happens is that the voters cast their ballots in each state for who they want to be president of the United States. Once all the votes have been cast and counted, ALL
the electoral votes of that state go to the winner of the popular vote within that state.
So lets say that in California, John Kerry gets 57% of the vote, and George Bush gets 34% of the vote, and independent candidates get the remaining 9% of the vote. Because John Kerry got a majority, all 55 electoral votes will be awarded to the Democratic party, and thus John Kerry will have "won" california. He now has 55 electoral votes to his name.
Now let's say that in Texas, which has 34 electoral votes, George Bush wins with 72% of the popular vote. (just as an example). Then all 34 electoral votes from Texas become his.
This continues, state by state, until the election is over. As a candidate wins a state, the electoral votes from that state become his. At the end of the election, whoever has won the most electoral votes, becomes President of the United States.
In the event of a tie, the supreme court will decide who becomes president, as far as I know. That almost had to happen in 2000, as it was unclear who had won florida. Lots of unaccounted votes made it hard to tell who won the popular vote in that state, and thus the electoral votes first went to Gore, then to Bush, and stalled there while recount after recount took place. The supreme court stopped the recount, leaving Bush with the electoral votes and the victory in the 2000 election. We may not ever truly know just what the final results in florida were. But, that's over and done with now.
Hopefully that will explain how it works.
I suggest to get a better idea you check out this page. It's an interactive map on John Edward's site which shows you who would have to win what states to get enough electoral votes to become president:
Check it out! 100% unbiased and educational.