The Navajo (Dine, in Navajo) are the 2nd largest (in population) American Indians tribe after the Lakota (Sioux). Based on linguistic evidence, the tribe is believed to have migrated into the United States on one of the last Indian migrations, sometime around the 1400s. They eventually settled on their homeland, the dinetah which exists across Colorado, New Mexico and Arizona.
The early Dine were hunter-gatherers who learned agriculture from the neighboring Pueblo Indians. Once settled as farmers, their religious lives, social lives, and substance places 4 crops as sacred: corn, beans, squash and tobacco, though the actual diet was supplemented by many smaller crops and gathered foods.
After the arrival of Spanish explorers the Navajo acquired sheep and horses, the sheep becoming as significant as corn in their daily and cultural lives, providing wool and meat as well as a consistent income from new technologies like weaving which they could sell to American traders and other tribes.
The Dine are animists, believe gods or spirits live within many (in some senses, all) things both living and non-living. They share a view of the world that is based on the concept of Hojoho or "Beauty", and believe that at the core of all health is walking a pure, righteous, beautiful and peaceful path in life. When you get sick, a medicine man (or more correctly, a Singer) will use the power of the Earth and the power of God to help cleanse the spirit of the tainted parts, and bring the person back to the "Beauty way".
Like many Indian tribes, many Navajo have found a path that incorporates Christianity into their traditional beliefs, especially the idea of One God which is emphasized far more than Jesus or the bible.