Please explain how the First-Past-the-Post system of voting works in the UK?

In the UK you have 650 constituencies, which means in the House of Commons you have 650 members of Parliament (MPs) and each one of these MPs represent their constituencies. On voting day each person is allowed to vote once for the candidate they like the most. The candidate with the biggest amount of votes wins the election and becomes the MP of that constitution. This means they have a seat in the Parliament where they debate and decide laws and bills. The role of the MP is to ensure that the best outcome for his/her constituents is reached and their views are represented.Many argued that FPTP may not be the best democratic system because of the idea of the winner-takes-it-all. This would suggest that if for example out of 70,000 people voting in a constituency 30,000 vote for candidate X and the rest 40,000 vote for candidates Y, Z or Q, candidate X would win even if the majority of people voted for other candidates. This is FPTP in a nutshell.