How did they discover America?

Answer 1

The continent now known as America was "discovered" by several entities. Among these are the Vikings, the Chinese, an Italian named Christopher Columbus who was working for the Spanish, possibly Polynesians, and ancestors of the Japanese the Ainu (Kennewick Man). Traditional archeology has it that nomads coming across the Bering straits were the first inhabitants, so the first "discoverers" may have been ancestors of the Mongols and Russian tribes.

Answer 2

They did not "find America", since Asia and the Americas were effectively one continuous land mass. They had no maps, no atlases, no Google Earth and no concept of different continents; they simply followed moving herds of game animals and gradually populated the Americas without ever realising it. For them it was the same as moving across the vast empty tundra of north-East Asia.