It takes years of hard work and political campaigning, and a lot of money is needed to do this.
But if you wanted to become president, what would you have to do? And what's in store when you finally get the job?
It doesn't matter if you are a man or woman, or what race or religion you are. However, there are certain things that you have to be or have done in order to be in line for the job. These are:
Normally, a person wanting to be president would have worked in politics before, but this doesn't have to be the case.
For example, Hillary Clinton used to be the US secretary of state, which is a job in the government. Her supporters say this makes her better qualified for the job of president.
Donald Trump is better known for being a successful businessman. His supporters think that it is time that somebody who wasn't a politician was given the job.
The American people decide who will be their president by voting.
However, if you want to be president, you have a lot of people to convince before you can get the job.
Once you have announced you want to be president, first of all you need to persuade your party to let you represent them. The Democrats and Republicans can only choose one person to enter the competition to be president for them.
You would do this through a series of votes called primaries and caucuses, which take place across the country in the first half of the election year.
At these, you need to win the support of people called delegates, who are people in your political party who have the power to vote for you to be a presidential candidate.
After the primaries and caucuses comes a big meeting called the party convention. At this, the delegates vote for who they like and both parties officially announce who they have chosen to represent them in the election. If you win this, you're halfway there!
After this, you would choose a running mate to stand by your side, who will be your vice-president if you win the election.
Then, you have to convince the people of America to vote for you!
This take weeks of hard campaigning, spending a fortune on advertising, travelling for many hours, giving many speeches and working extremely hard all over the country.
Once you've done this, you need to hope that they vote for you in the election! If you win this vote, then you will finally become president and officially start the job on 20 January the following year.
Given that the US president is perhaps the most powerful person on the planet, it is far from an easy job. The president is in charge of the most powerful country in the world.
He or she suggests laws and how much money the country should spend. He is automatically made commander-in-chief of the US army and generally responsible for how the US deals with other countries. He also oversees the national US government.
The president also chooses the judges who will work in the Supreme Court. Although, the Senate has to agree to these.
Everything you do and say as president is very carefully watched. There will be many people that will agree with you, but many that don't - so the president must be ready to receive a lot of criticism throughout their time in the job.
It's certainly not easy!
The road to becoming president is a very long one.