Complex sentence: The initial NBP is a Boot Manager able to retrieve its own configuration and deploy a menu of booting options after the user selects a booting option an OS dependent Boot Loader is downloaded and run in order to continue with an specific booting procedure.
Split into simpler sentences: The initial NBP is a Boot Manager able to retrieve its own configuration and deploy a menu of booting options. The user selects a booting option and an OS dependent Boot Loader is downloaded and run in order to continue with the selected specific booting procedure.