First, it is extremely important to distinguish between Indians (people from India) and Native Americans. Indians did not migrate to the United States in significant numbers during the colonial period; in fact, immigration from India to the United States only became significant in the twentieth century, during which Indian-Americans became one of the ethnic groups with the highest educational levels and earnings in the US population.
Native Americans, on the other hand, lived in North America long before the advent of Europeans, and had a deep familiarity with local flora and fauna. The survival of many of the early colonies depended on trade with Native Americans and on European settlers acquiring local knowledge from Native Americans.
The relationships between Europeans and Native Americans varied from colony to colony, with some seeing trade, especially in furs, as a source of profit and cultivating alliances with individual tribes. Other colonies came into territorial conflict with Native Americans and even outright war, and deliberately attempted to eradicate their populations. As Native Americans had not been previously exposed to smallpox and other European epidemic diseases and had no biological immunity, epidemic diseases, whether introduced deliberately or accidentally, decimated Native American populations.