(CNN) It may be a long, raucous and rambling road to the White House , but choosing the next American president is anything but simple.

While many voters won't pay attention until a few weeks before Election Day, running for president takes years of active planning, fundraising and calculation.

But when should you start caring? And what's the difference between a caucus and a primary? Here's what you need to know about the 2016 U.S. Presidential election.

Why do U.S. presidential elections take so long?

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America's two main political parties -- Democratic and Republican -- choose their respective nominees through party-sponsored contests in each of the states and U.S. territories, a process that starts in February and takes up to five months.

Iowa and New Hampshire traditionally kick off the process early in the year, and then other states follow -- but before that, candidates have typically spent a year laying the groundwork for campaigns in those regions.

Once each party has a candidate, they spend the rest of the summer and autumn campaigning until the general election on November 8.

Why do they cost so much money?

One reason they cost a lot is because they last so long. Unlike some other countries, there are no rules on how early a candidate can start campaigning -- Ted Cruz officially announced he was running in March 2015, nearly 20 months before the election.

Also unlike some other countries, there's no limit on how much you can spend. A presidential campaign can cost up to $1 billion -- and that's not even counting money spent by outside groups. It's not cheap to travel across the country for two years or more, buy advertisements on television, and pay a small army of campaign workers.

What's the difference between a "caucus" and a "primary"?

States have two ways of collecting their party members' votes when choosing a presidential candidate -- "primaries" and "caucuses."

A "primary" is what most people traditionally think of when they imagine voting -- people show up at a neighborhood polling place to vote for their candidate by ballot.

A "caucus" is very different. It's a neighborhood event that requires several hours of active communal participation and debate, and takes place in the evening in a home or public space, depending on the size of the caucus location.

When should I start caring?

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Thirteen states and territories held caucuses or primaries on the first Tuesday in March -- also known as "Super Tuesday." The results cemented Hillary Clinton and Donald Trump as the clear favorites in the race for the Democratic and Republican nominations, but it's far from over.

So who are the top Republican contenders?

Donald Trump: The real estate mogul has led the field for months despite breaking many rules of traditional campaigning, including criticizing prisoners of war, Mexicans, Muslims and women (amongst others). Very few experts predicted he would be so successful.

Ted Cruz: The fiercely conservative Texas Senator has made a name for himself as an outsider in Congress. He orchestrated a government shutdown in 2013.

Marco Rubio: The Florida Senator came to power with the rise of the anti-establishment "Tea Party" side of his party in 2010, but has shown ability to work with Democrats.

And who are the top Democrats?

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Hillary Clinton: She's been planning this campaign almost since the moment she lost in 2008. Wife of Bill, she's seen as somewhat of a continuation of Barack Obama and a safe pair of hands by Democrats.

Bernie Sanders: The Vermont Senator represents the most liberal wing of mainstream American politics, but some Democrats see him as too lefty to win a national election.

When will we finally know who the nominees will be?

We usually know who the party nominees will be by late spring, but they are not officially chosen until the national party convention in the summer.

Does the nominee with the most votes win?

If only!

Instead of selecting a president based on how many votes they receive, the Founding Fathers established what's called the Electoral College. Each state gets the same number of electors as it has Congressmen and Senators -- and the bigger the state, the more electors it has.

In all but two states (Maine and Nebraska), it's a winner-take-all system -- so if you win 60% of the vote in California, you get all of that state's electors. For example, in 2012 Obama got 51% of the nationwide votes, which translated into 61% of the Electoral College votes.

In the end, whoever receives 270 Electoral College votes or more wins. Don't even get us started with what happens if there's a tie -- and we already know what happens when there's a recount.