The United Kingdom is made up of England, Scotland, Wales and Northern Ireland (it's actually officially "The United Kingdom of Great Britain and Northern Ireland").
There is no simple answer to your question. When people are asked where they are from, they might say England, they might say Britain, they might say the UK.
"England" should not be used if someone is actually talking about Scotland or Wales, nor if they are talking about Britain or the UK. However, some people will use it.
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