What is Linux and why we have to use it

what is linux ?  LINUX is freeware. anyone can view and edit the source code of OS It is fully customizable.
Most Important Feature is Stability, multitasking, multi-user,LINUX has better security structure.High Portability Easy to port new Hardware Platform Written in C which is highly portable.

Kernel:
Kernel is the heart of the operating system.It is the low level core of the System that is the interface between applications and H/W.
Functions
Manage The Memory, I/O devices, allocates the time between user and process, inter process communication, sets process priority.

Shell:
The shell is a program that provide interface to users for their commands.
It is a command interpreter and also has programming capability of its own.
Shell Types

  Sh  (First shell by Stephen Bourne at AT&T bell labs in 1977)
  Bash  C Shell(sh)
  Korn Shell (ksh)

File System:

Linux treats everything as a file including hardware devices. Arranged as a
directory hierarchy.

The top level directory is known as “root (/)”.

/bin    Essential command binaries
/boot    Static files of the boot loader
/dev     Device files
/etc     Host−specific system configuration
/lib     Essential shared libraries and kernel modules
/media     Mount point for removeable media
/mnt     Mount point for mounting a filesystem temporarily
/opt      Add−on application software packages
/sbin      Essential system binaries
/srv      Data for services provided by this system\
/tmp      Temporary files
/usr     Secondary hierarchy
/var     Variable data.