How does the British electoral system work?

The electoral system used in the United Kingdom is called First Past The Post. When the UK Government calls an election, we vote in our constituencies to elect representatives for the House of Commons, which are called 'Members of Parliament' (MP). There are 650 constituencies in the UK, therefore each area will vote for one representative of their geographical area.
Voters can only vote for one candidate, marking an 'X' next to the candidate's name on the ballot paper. First Past The Post is a 'plurality' system, which means that the candidate who wins the most votes is elected. Under this system, therefore, a candidate can win with less than half of the constituency's support: if there are 5 candidates, and the vote split is 10%, 20%, 30%, 11%, 29%, the candidate with 30% of the vote will win the role of MP for the area.
To form a majority government, a political party needs to have a minimum of 326 seats. If no party reaches this threshold, then they may have to consider entering a 'coalition', where they 'team up' with other parties to reach that threshold.