Windows Boot Manager is a crucial component of the Windows operating system that helps manage the startup process of a computer. It is responsible for loading the operating system and providing options for users to select different operating systems or recovery tools if multiple options are available. When a computer is powered on, the Windows Boot Manager initializes and checks for installed operating systems. If Windows is the only OS, it will load it automatically. If there are multiple systems, it presents a menu for users to choose which one to start, ensuring a smooth booting experience.