The term "commander-in-chief" refers to the role of the president as the highest-ranking officer in the military. This means that:
The president has the power to give orders to all uniformed military officers.
While the president does have significant authority in military matters, including influencing military budgets and strategy, the power to declare war is constitutionally vested in Congress. The president's role as commander-in-chief primarily pertains to leading the military and making command decisions.