How does the health insurance work in the UK?

Is there a government health insurance for every employee in the UK? How much do you pay per year? Is it deducted from your paycheck? Can you get additional health insurance? Are vision and dental usually included as a benefit from your employer? I am moving to the UK and would like to know a bit more about what to expect. Thank you!
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The NHS (National Health Service) is either free or very cheap: the idea is that everyone can use it. Although the UK is a wealthy country, the NHS has many issues: if you have an accident, you could find yourself waiting for much longer than you expect to get surgery or an examination. There are lots of delays and some misdiagnosises, but the doctors are very good, and carry out very complex surgeries very efficiently. If you can afford it, there is private insurance, and different clinics range in insurance price, and there is travel insurance. I'm only 15 so I'm still not entirely sure how it works, but this is a basic overview. Hope this helps.
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