Why was the discovery that the world is round so important? And how did it help humanity?
Lots of people had the idea in the 1400s that you could reach the east by going west, but they greatly underestimated the diameter of the earth so they didn’t realize how far it would be. And of course they didn’t know there was another continent in the way. That’s why Columbus thought he was in India or Japan.
For years after that people tried to find a way -around- the New World to get to the Far East, which was the idea in the first place. They had no idea how wide the new continent was! A lot of explorers sailed up rivers on the East Coast, hoping they might go all the way across the continent. Some sailed between the islands of northern Canada looking for a ‘Northwest Passage’. None of these people were successful.
It was Magellan who finally figured out how to get around the New World by sailing around the tip of South America.
Magellan himself didn’t make it. He was killed in the Philippines. But his expedition was the first to actually go all the way around the world, proving once and for all that it could be done. The passage south of the southern tip of South America is still named after him.
There’s a good article about Magellan on Wikipedia that has lots of interesting stuff about him.