Christopher Columbus was born in 1451 in Genoa Italy. His brother Bartolomeu got a job as a mapmaker in Lisbon, Portugal, which was at the centre of the efforts to find a sea route to India, and Christopher, a sailor, joined him there, hoping to get a job in the new industry of exploration. Portugal's navigator prince, Prince Henry, had set up an academy devoted to navigation in southern Portugal, and Portuguese ships began to explore the Atlantic ocean, reaching the Azores islands and gradually mapping out the western coast of Africa.
Columbus was eager to join the navigators, and petitioned the King of Portugal John II, to finance his expedition to find a sea route to India by sailing in a western direction. However, a Portuguese man Bartholemeu Dias sailed east and southwards, along the coast of Africa, and managed to sail round the southern tip of Africa, the Cape of Good Hope. The King concluded that sailing east was more likely to get his ships to India than sailing west and declined Columbus' petition for finance for a western expedition.
In desperation Columbus turned to Ferdinand II and Isabella I of Spain, who had been watching the Portuguese expeditions with envy and were keen to get in on the action. If the Portuguese had gained control of the easterly route to India, Spain thought it worthwhile to try to gain the westerly route if one existed, though they were unsure if the expedition would work. Columbus was given his money and his ships set sail.
He reached the West Indies in 1492, and capturing some natives, sailed back to Spain. He made three more voyages, discovering more of the West Indies each time, and setting up Spanish bases, and on the fourth voyage he finally made landfall on Central America.
The Spanish crown had not expected him to return, and promptly reneged on some of the profits he should have earned from his discoveries. He and his brothers were also accused of tyranny and removed as governors of Hispaniola. His descendants spent decades in court trying to get the Spanish crown to honour it's contracts. To his death Columbus thought he had discovered a westerly route to India. It was his successors, on making further expeditions from the bases Columbus set up in the West Indies, who realised that in fact he had discovered a new continent. Columbus wasn't the first European to have sailed west, but he was the first to set up sustainable bases in the Americas, which in turn led to that entire continent being colonised.
In modern times Columbus has fallen in stature - he was a nasty racist who commited genocide over the people he met - the Spanish monarchs were justified in accusing him of nastiness and tyranny. But the Americas (including the USA) would not have become a thing without him. Such is the murkieness of history.