Why were the Native Americans so important in the clash between the French and the British?

Much of the French and Indian War was fought on the British and French frontiers of North America. At the time, little was known of this heavily-forested area to most Europeans and colonists. Because of this, it was important for both sides to have Native American allies.
These Native allies helped their respective sides in a number of ways. They served as scouts, guiding European forces through unknown territories. They also formed raiding parties that could disrupt the supply lines of the enemy. Importantly, they were accustomed to wilderness warfare, something that few European soldiers had experience with. As a result, they proved very helpful when fighting in the dense forests of the frontier.
While the British had Native allies, the French relied on their Native allies more. Many Native peoples were concerned with British expansion. At the start of the conflict, there were 1.5 million English in North America, compared to less than 100,000 French. The French were seen as less of a threat to Indigenous peoples. Therefore, they had the cooperation of many Native peoples, including the massive Confederated Nations of Canada, in confronting the British. The French were eager to get this help as well, as they had a much smaller fighting force than the British.
https://history.state.gov/milestones/1750-1775/french-indian-war

I am assuming that you mean the French and Indian War which took place between 1756 and 1763.  Native Americans were highly valued by both the British and French during the war, and the European powers were able to use tribal animosities to their advantage during this conflict.  Native Americans knew the territory and could be used as scouts and guides for invading armies.  They could also be used to attack colonial settlements.  British and French armies fought in linear formations and had to observe the laws of war; however, their Indian allies were not bound by these laws, and these native groups could be used to terrorize local civilian populations.  This happened often, especially in western areas.  Native groups could also attack the supply lines of the main armies.  Neither the British nor the French planned on maintaining long-term partnerships with these tribes after the war, but both nations used native warriors for their own benefit.