1. Ans: The 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. Ans: We use commands for performing various tasks.

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

4. Ans: 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.