I guess this is relatively on topic, so I'll explain.
The first past the post system is where the person with the most votes wins, period.
However, this can easily result in large amounts of gerrymandering, unproportionate representation, and minority rule.
Let's assume there are 8 candidates who can run. The first gets 5%(1st) of the vote, the second gets 10%(2nd) of the vote, the third gets 12%(3rd) of the vote, then 15%(4th), 21%(5th), 19%(6th),13%(7th), 5%(8th) respectively.
In FPTP, whoever got 21% of the vote would win automatically, even if those who voted for the 6th, 7th, and 8th candidates, all would have rathered the 6th candidate over the 5th who won. So, in the next election, they strategically all vote for the 6th candidate.
Likewise, the 1st, 2nd, and 3rd voters all would have wanted the 4th candidate over the 5th. So they all strategically vote for the 4th candidate next time.
Now the vote becomes:
4th: 42%
5th: 21%
6th: 37%
Now, this time, the 4th candidate wins.
In the next election, the people who voted for the 5th candidate are split. They know that 5th candidate won't win again, so they all vote for the candidate they'd rather instead. As a result, 7% of them go to the 4th candidate, and 14% go to the 6th candidate. During the next election it becomes:
4th: 49%
6th: 51%.
Seem familiar? And, over time, votes always select either candidate #4 or Candidate #6, with #5 voters being the swing voters, which are slowly becoming more partisan over time.
Now, let's say the 7th candidate decides to try to run again.
4th: 49%
6th: 39%
7th: 12%
Now the 4th Candidate wins, even if all those who voted for the 7th candidate would have rathered the 6th candidate. This is known as the spoiler effect. Additionally, a good amount of #7's campaign funding came from voters who supported the 4th candidate, knowing that it would spoil the vote and increase their chances of winning.
This, is the state of elections we have today. A two-party system with third-party candidates typically just spoiling the vote.
A single Transferable Vote system would work much better, however, that's extremely complicated to explain in words, and I'm running short on time. I'll try to explain it better later, or you can try to look it up. Note, that the STV system applies to votes where multiple people are elected, like house or Senate positions, not positions like the president.