The story of how English came to be, does not start with that island off the north-west edge of Europe. The English were a German barbarian tribe from Asia. About two thousand years ago many of these barbarian tribes started moving into Eastern Europe. Why is not clear, but it has been speculated that the rise of China as a great country was pushing these wild tribes to move some place else. The Great Wall and the rise of China may have pushed the original English out of Asia.
The English tribe, called the Angles, were one of the German tribes that moved into the middle of Europe. The Angles were a Low German tribe who lived in the low lands near the sea. The High German tribes lived in the hills. The Angles lived on a part of the coast that looked bent into the shape of a fishhook. The Old English word Angul meant hook and to bend into such a shape. (This is also the origin of the Modern English verb angle meaning to fish and the space between intersecting lines in geometry class.) The Angle tribe were a violent people who liked war. They were also an unhappy people. They lived in a small poor piece of land shaped like a fishhook. Their neighbours, the Saxons and the Franks, were too difficult to kill.
At the time, tribes like the Angles fought with the people who lived in Europe. The Roman Empire had to fight many wars to stop the invading barbarians. Too often the Romans lost. Tribes like the Franks invaded the Roman province of Gaul and renamed it France.
Meanwhile in the Roman province of Britain, the Roman army left to go fight the barbarians (and other Romans) elsewhere. The British were in trouble; they were a civilised people who did not do a lot of fighting. They spoke the language Old Brittonic, although educated people learned the Roman's Latin language. With the Roman army gone they needed to form kingdoms and create new armies to fight off the invading barbarians.
About 1500 years ago the British King Vortigern hired some Angle fighters to come and help him fight some other barbarians called the Picts. He used the strategy of using barbarians to fight each other. It did not work! The Angles liked Britain so much that they brought their friends the Saxon tribe (meaning the strong tribe) with them and invaded Britain for themselves. The British either ran away to the hills in places like Wales or learned some English words.
The Angles were not a civilised people. They did not build houses with more than one floor. They thought that reading and writing was some type of magic. They did not understand how life in a city worked. All these people in one place left no space for farming or hunting. The British understood that one person who was very good at making clothes might make clothes and sell them to others for food. A British person making many clothes did not need to farm, fish or hunt. Angles who did not farm, fish or hunt did not eat.
Eventually the Angles, now called the English, learned how city life worked. The British learned to speak some English. The Old English language was born by Old Brittonic speakers using their own grammar and the new English words. From the beginning, people learned English as a second language.