Linux

is an open source operating system. 

the operating system is the software that directly manages a system's hardware and resources, like CPU, memory and storage.

Direct access to a computer. It where yo ask software to perform hardware actions that point and click graphical user interfaces simply can't ask. 

Linux Command line and open source software, together give users unrestricted access to their computer.

Every Linux-based OS involves the Linux Kernel which manages hardware resources and a set of software packages that make up the rest of the operating system.

The base component of the OS, without it the OS doesn't work. The Kernel manages the system resources and communicates the hardware. It is responsible for memory, process and file management

Administrative layer of the system-level tasks like configuration and software install.  This includes the shell or command line, daemons, processes that run in the background and the desktop environment

a type of software that lets you perform a task. Apps include everything from desktop tools and programming languages to multiuser business suites.  Most linux distributions offer a central database to search for and download additional apps

• Memory management 
• Process management 
• Device drivers
• System calls and Security

keep track of how much memory is used to store what and where

determine which processes can use the central processing unit (CPU), when and for how long

act as the mediator/interpreter between the hardware and processes

receive requests for service from the processes the kernel, if implemented properly, is invisible to the user, working in its own little world known as kernel space, where it allocates memory and keeps track of where everything is stored.  What the user sees-like web browsers and files - are known as the user space.  These applications interact with the kernel through a system call interface (SCI) 

The kernel issues a busy personal assistant for a powerful executive ( hardware.  If assistant's job to relay messages and requests processes from employees and public users to the executive, to remember what is stored where (memory), and to determine who has access to the executive at any given time and for how long.

• Hardware
• The physical machine—the bottom or base of the system, made up of memory (RAM) and the processor or central processing unit (CPU), as well as input/output (I/O) devices such as storage, networking, and graphics. The CPU performs computations and reads from, and writes to, memory.

• Linux kernel
• The core of the OS. (See? It’s right in the middle.) It’s software residing in memory that tells the CPU what to do.

• user processes
• These are the running programs that the kernel manages. User processes are what collectively make up user space. User processes are also known as just processes. The kernel also allows these processes and servers to communicate with each other (known as inter-process communication, or IPC).

Code running in the kernel mode has unrestricted access to the hardware, while user mode restricts access to the CPU and memory to the SCI. A similar separation exists for memory (kernel space and user space). These 2 small details form the base for some complicated operations like privilege separation for security, building containers, and virtual machines.