The first polls in the US presidential election will open on Tuesday (Nov 8) at 1pm, Singapore time. Polls across the 50 states will close by Wednesday afternoon, Singapore time.

If you've not been following the long-drawn-out campaign, or the ups and downs on the trail, this primer will bring you up to date with what to watch out for:

Who are the candidates?

All the attention has been focused on the two major party candidates, Democratic Party nominee Hillary Clinton and Republican nominee Donald Trump, but there are actually two other party candidates running - Libertarian Party nominee Gary Johnson and Green Party nominee Jill Stein.

There is also an independent named Evan McMullin making waves in Utah. Neither of the minor candidates have any chance of winning but the size of their vote share could well have an impact on the final result.

Who is going to win?

The gap between the candidates has closed in the past week, with Mrs Hillary Clinton now holding a narrow lead over Mr Donald Trump.

The RealClearPolitics polling average one day before the result gives Mrs Clinton a 2.2 percentage point lead nationwide. Forecasters say the lead translates into a chance of winning anywhere between 65 per cent (FiveThirtyEight) to 99 per cent (Princeton Election Consortium).

In betting markets, Betfair gives Mrs Clinton an over 80 per cent chance of winning.

While these numbers look good for Mrs Clinton, the large range is a sign of the degree of uncertainty. One can never rule out a shock in an election where anything that can happen has happened.

What have been the main issues of this election?

At different times in the past year, issues like free trade, jobs, immigration, national security and who gets to appoint Supreme Court justices have crept into the conversation, but this campaign has primarily focused on scandals and personalities.

For Mrs Clinton, her e-mail scandal and how trustworthy she is have been the key points for voters. For Mr Trump, the focus has mainly been on the allegations of sexual assault against him and the question of whether or not he has the temperament to be president.

History will be made, whoever wins

Whether it is Mr Trump or Mrs Clinton who is victorious on Nov 8 (Wednesday Nov 9, Singapore time), the winner will make history. A President Trump will be the first ever political outsider to be elected president in American history.

At 70, he will also be the oldest first-term president. If Mrs Clinton, 69, wins, she will be the first woman to be elected president.

How a president is picked - a primer on the electoral college system

Though polls leading right up to the presidential election measure the relative support each candidate has from voters, the actual winner will not be determined by the popular vote.

Rather, in a process unique to the US, it is an electoral college that will pick the president and vice-president. Every state is allocated a certain number of electors based on its population. And in nearly every state, electors are awarded to presidential candidates on a winner-takes-all basis.

For instance, whoever wins the popular vote in Florida will get all 29 of its electoral votes. Maine and Nebraska, however, split their electoral votes. The winner is whoever wins a majority of the 538 electors - at least 270 votes.

The structure of the electoral college has major implications on how candidates approach elections. Because the margin of the popular vote doesn't matter, candidates tend to ignore states where they are assured of winning the popular vote. They then focus all their energies on states where the contest is close.

That's why states like Texas and California - among the country's most populous - hardly attract any attention.

What are the swing states?

According to the latest polling, the states that face the closest fights this election are Florida, North Carolina, Ohio, Nevada and Iowa. They are followed by the likes of Pennsylvania, New Hampshire, Colorado and Arizona.

These are the states where the candidates have spent the most time campaigning and where most of the resources have been poured into. The biggest prizes among the toss-ups are Florida, North Carolina and Ohio and whoever wins there will stand a good chance of becoming the next president.

What to watch for as results come in?

If Mrs Clinton carries all of these states, she clinches the White House. Adding these closely-contested states to those that are solidly Democratic will put her past the 270 needed to win. But if one or more of these states go to Mr Trump, then the race could go his way.

That would make for a long, nail-biting night as the results trickle in.

Each of these three battleground states, which have the most number of electoral votes, could be decisive. Mr Trump needs to sweep them all if he is to win. Mrs Clinton can afford to lose all three and still win the election provided the other states back her up.

Nearly every poll currently shows Mr Trump trailing, albeit closely in some. His most viable path to victory involves a sweep of all toss-up states. So, if Mrs Clinton takes these states which currently lean Republican, then Mr Trump is in real trouble.

Nov 9, 11am onwards: Will the loser concede?

Major TV networks tend to predict one of the candidates has won much before officials do.

In previous elections, this has happened as early as 9am. In the past three elections, the winner was declared between noon and 12.30pm. But if the result is contested, it could even take weeks, like in 2000 when Mr George Bush and Mr Al Gore were locked in a close battle. Given the bitter race and talk of a rigged election, this year, watch if this sequence is followed.

Where can you watch the results come in?

You can get the latest election news from our website www.straitstimes.com and follow the action on our special live blog str.sg/usliveblog, as well as on www.facebook.com/TheStraitsTimes/ and on Twitter @STcom starting from 6.30pm Singapore time on Tuesday, when most polls will open for voting in the US.

You can also watch the coverage on BBC World News, CNN, CNBC, Fox News Channel and Sky News.