The command line is a type of user interface which allows the user to interact with the computer by typing in commands.
You open it in Linux by selecting ‘Terminal’ from the menu.
This will open a box into which you can type text.
If you type the right text then your computer will understand you and do what you ask it to.
You do not need to understand the text in order to be able to cut n’ paste it into the box – so long as the person who is telling you what to type understands what they are doing.
Most new Linux users are reluctant to use the command line at first; however, it is actually very easy and experienced users will often refer to it as your best friend.
If you do want to learn much, much more about how to use the command line, then visit this page.