Ntoskrnl is the operating system kernel for Windows. It is an essential part of Windows. The kernel is responsible for providing secure access to the machine's hardware to various computer programs. It controls the way any other software component can access these resources.
The boot sequence is the order of the processes and steps requires to start a computer. After you turn on the computer it goes through its power on self test (POST) which is a diagnostic program that checks your hardware to ensure that everything is present and working properly. Then the BIOS checks devices, finds the boot sector and shows its startup screen.
Then the boot files are located on the hard drive and the proper boot sequence is initiated by the boot loader which loads other software for the operating system to start. The boot sectors main function is to load and execute the kernel which continues startup. Finally the operating system is loaded. The process will vary depending on the operating system in use.