The UK encompasses Scotland, England, Wales, and Northern Ireland.
Great Britain encompasses England, Scotland, and Wales.
The best way to remember it is that Great Britain is the whole land mass, whereas the UK has a portion of the emerald island.
England is its own sovereign country.
England came first as its own country after the Anglo Saxon kingdoms merged.
In 1707, it merged with Scotland to become the Kingdom of Great Britain.
In 1800, Ireland merged.
Then in 1922, southern Ireland won their independence from the English and established the Republic of Ireland.