What belong to Great Britain?

Answer 1

Great Britain means the countries of England, Scotland and Wales - including the Hebrides, Orkney, Shetland, the Isle of Wight, the Scillies and many other smaller islands.

The Sovereign State of the United Kingdom of Great Britain and Northern Ireland consists of Great Britain and the Northern part of the island of Ireland.

Note that the Isle of Man (between Scotland, Wales and Ireland) and the Channel Islands (just off the North coast of France) both have unusual status. Although they share much in common with the UK, they are technically not part of Great Britain or the UK (or of the EU).