1.    What is Command?

a command is a directive to a computer program to perform a specific task

2.    Why we use command?

Using a command line, you can perform almost all the same tasks that can be done with a GUI.

3.   How can we find detail information of any command?

man "command name"

Explanation: UNIX provides us with a facility of man command, which is used for getting documentation of any command.

 list of essential "file" commands 

mkdir - to create any folder

rmdir - to delete any folder

rm -r - to delete any folder if their is any file under in it

cp - to copy any file from one to another path

mv - to move any file from one to another path

echo - to print something

gzip - convert any file to zip

gunzip - convert any zip file to its usual format

touch - to create any file with any extension like .txt etc.

nano - to open a text editor to edit the text under the file

cat - to show the text under the file into the terminal

cat>> - to append two files text/data into one

ls -l - to check the permission of files under the pwd

chmod - to change the mode of any files like read , write or execute .