The impact of disease on the Native Americans was widespread and terrible, many of them ended up dying from diseases.
When Europeans started to discover and venture to the Americas, they started to be in contact with the Native Americans. Remember, the Native Americans had no contact with people from other countries and had never contracted such diseases, meaning they did not have any immunity from them. Since Europe was vast and contained a lot of different people, the people had more of an immunity to diseases like smallpox and measles.
When the Natives continued to have contact with the Europeans, they started contracting these diseases. Since they did not have a proper immunity against them, this caused many to die.