Kernel is the central core component of a Unix operating system (OS).
A Kernel is the main component that can control everything within Unix OS.
It is the first program that is loaded on startup of Unix OS. Once it is loaded it will manage the rest of the startup process.
Kernel manages memory, scheduling as well as communication with peripherals like printers, keyboards etc.
But Kernel does not directly interact with a user. For a new task, Kernel will spawn a shell and user will work in a shell.
Kernel provides many system calls. A software program interacts with Kernel by using system calls.
Kernel has a protected memory area that cannot be overwritten accidentally by any process.