1. A command is an instruction given by a user telling a computer to do something, such a run a single program or a group of linked programs.

2. We use commands for performing various tasks.

3. One may use the "man 'command_name'" command to find out more about a particular command.

4. Some of the essential file commands and their use are:

nano- to create a new file

cat - for joining two or more files and seeing the combined output

mv - to move a file from one place to another, can also be used for renaming

rm - for removing/deleting a file

cp -  for copying a file from one place to another

grep - for searching a specific keyword

gzip - for compressing a file

gunzip - for decompressing a file

echo - for displaying various information