Columbus was definitely not the first person to discover America. In fact, America was discovered at least 10,000 years before Columbus arrived in the New World, and probably much earlier. Columbus was probably not even the first European to reach America. Additionally, although he possibly did briefly visit what is now Venezuela in South America, Columbus never even set foot on the North American continent.
The first people to discover and settle America were the ancestors of the Native Americans, who had already established complex civilizations in North and South America by the time the Europeans arrived. Scientists are still studying exactly when and how the first Native Americans made it to America. For a long time, the theory was that they were Siberian Asians who migrated across the Bering Land Bridge about 15,000 years ago. Modern DNA studies suggest that these people may have not have migrated directly from Asia, but rather may have lived on the Bering Land Bridge for thousands of years until the end of the most recent ice age and then journeyed into North America. Other theories posit that the original Native Americans traveled from Japan or other parts of East Asia by boat.
As far as the European discovery of America, many historians attribute that to the Viking Leif Erickson, who arrived in North America about 500 years before the time of Columbus. Leif Erickson's father, Eric the Red, settled on the island of Greenland, which is not far from Canada. Erickson explored parts of the east coast of Canada and spent an entire winter there before returning to Greenland. After this, other Vikings journeyed to Canada over the next decade or so. They possibly did not follow up on these trips because of the violent encounters they had with the Native Americans who were already there.
Although Columbus did not discover America, the importance of his expeditions lies in the fact that he made European rulers aware of the lands to the west and initiated the widespread settling of North and South America by Europeans.