"United Kingdom" is a sovereign state made up of different countries. These are England, Scotland, Wales and Northern Ireland.
"Great Britain" is often used to refer to England, Scotland and Wales. It is a geographical -rather tan a political- term.
"England" is a nation of the United Kingdom. England is often confused with the United Kingdom as a whole because it is the largest and most populous of the nations and contains the de facto capital city, London.
Am I right? Please, correct me if I make any mistake.
I've realised that it's an absolute faux pas to say that someone from, say, Scotland, is from England. That might cost you a good relationship. In my language there is usually not made much difference between using the word for 'Great Britain' and 'England' so we sort of say 'England' for the entire island in daily speech (maybe this is because 'England' is blocking the view of the other countries from my viewpoint here on top of the globe, or maybe it is just good 1000-year old tradition dating back to the Danelaw, or whatever). Anyway, I've realised that one must be careful and call someone from England an Englishman, from Wales a Welshman, and so on and so forth. And not claim them to be a Great Britainer or something to that effect.
It is even worse with people from Croatia, I once by mistake and slip of tongue mixed up Croatia with Bosnia and it nearly cost me the relationship with my colleague. I could literally feel an ice wall being erected right there and then, but I was later forgiven for my mistake. After that I kept a printed map in my top desk drawer with an X marking his summer house outside of Zagreb, lest I would forget.
Well the nation is actually called the United Kingdom of Great Britain and Northern Ireland. Which seems to fit in with your basic structure.
But there a lot of small bits left over. For example
Isle of Man
They belong to the Crown but not to the Nation........
You are entirely correct, Ana.
Many people in Scotland are interested in leaving the United Kingdom. The English verb for such a political separation (the same kind desired by some in Pais Vasco, Catalunya or Andalucía) is "to secede."
"Many people in Scotland would like to see their country secede from the United Kingdom."
"There is a strong secessionist (adjective from "to secede) movement in Scotland."
You'll hear many English people refer to England when they mean the UK. The UK is the sovereign state, which London is the capital. The UK is not England.
Scotland, NI and Wales are countries within the UK just like England is. The main difference is that most of the decision making power for all four countries lies in London, which is also the capital of England. Scotland, NI and Wales have difference degrees of power, but for anything big like going to war the decision is taken in London (not Edinburgh, Cardiff or Belfast - the capitals of the other countries).
It's a sore point at the moment (Brexit and Scottish independence), so it's good that you are checking.