A UK general election is not a single national contest. It is 650 separate constituency elections held on the same day, each choosing one Member of Parliament for the House of Commons.
What voters actually vote for
Each voter chooses a candidate in their local parliamentary constituency. You do not directly vote for a Prime Minister, and there is no separate national ballot for a government. The candidate receiving the most votes in each constituency becomes its MP.
Those 650 local results determine the composition of the House of Commons. A party with enough MPs to command the confidence of the House can form a government.
Why 326 is often quoted
With 650 Commons seats, 326 is the mathematical halfway point plus one. It is therefore commonly described as an absolute majority. In practice, parliamentary arithmetic can differ because the Speaker does not normally vote and some elected MPs may not take their seats.
How the winner is decided in each constituency
Westminster uses First Past the Post. Voters mark one candidate and the candidate with the largest number of votes wins. The winner does not need more than 50% of votes cast.
This means national vote share and seats can look very different. General elections are decided by who comes first in individual constituencies, not by allocating 650 seats in proportion to the UK-wide vote.
What happens after the votes are counted?
Where one party has a clear Commons majority, government formation is normally straightforward. Where no party has a majority, there is a hung Parliament. Parties may negotiate a coalition, a confidence-and-supply arrangement or a minority administration.
The constitutional test is whether a government can command the confidence of the House of Commons. The monarch appoints the Prime Minister under constitutional conventions; voters do not separately elect the holder of that office.
How often are general elections held?
A Parliament cannot continue indefinitely. Under the current dissolution framework, Parliament is automatically dissolved five years after it first met if it has not already been dissolved. An election can take place earlier following a dissolution requested by the Prime Minister.
General election versus devolved elections
A UK general election elects MPs to Westminster. It is separate from elections to the Scottish Parliament, Senedd and Northern Ireland Assembly, which use different electoral systems.
In short: 650 local contests produce 650 MPs; those MPs determine who can command the Commons and form a government.
Sources and further reading
UK Parliament: General elections ↗ · Electoral Commission: How MPs are elected ↗