Many thousands of years ago, not a single human being lived in the Americas.
This only changed during the last Ice Age. It was a time when most of North America was covered with a thick sheet of ice, which made the Americas difficult to inhabit.
But at some point during this time, adventurous humans started their journey into a new world.
They probably came on foot from Siberia across the Bering Land Bridge, which existed between Alaska and Eurasia from the end of the last Ice Age until about 10,000 years ago. The area is now submerged by water.
There is still debate about when these first Americans actually arrived and where they came from. But we are now getting closer to uncovering the original narrative, and finding out who these first Americans really were. During the peak of the last Ice Age about 20,000 years ago, a journey from Asia into the Americas would not have been particularly desirable. North America was covered in icy permafrost and tall glaciers. But, paradoxically, the presence of so much ice meant that the journey was, in a way, easier than it would be today.
The abundance of ice meant that sea levels were much lower than they are now, and a stretch of land emerged between Siberia and Alaska. Humans and animals could simply walk from Asia to North America. The land bridge was called Beringia.