Simply put, all three characters had a significant impact on Jamestown.
First of all, the Indians were hostile towards the men at Jamestown. In 1605, Powhatan, a very powerful chief of a confederacy of Indians called the Virginia Algonquians, had arrested John Smith and was going to have him killed. Pocahontas, his favorite daughter intervened and pursuaded her father not to kill him. She also pursuaded her father to give the settlers a chance and trade with them. He did, and the two sides agreed to get along. Later, the marriage of Pocahontas and John Rolfe temporarily united the two rival factions for several years.
I believe these events led to the eventual success of Jamestown as a permanent colony in the New World.