What does `man` command do?

The man command is one of the most important tools in Linux—it stands for "manual."

It is the built-in interface for viewing the system's reference manuals. Whenever you are unsure about how a command works or what its options (like -n) do, you use man.

How to use it:

To see the manual for a specific command, type man followed by the command name:

man cat

What happens next?

When you run a man command, an interactive viewer opens. It usually includes several sections:

• NAME: The name of the command and a brief description.
• SYNOPSIS: How to correctly type the command (its syntax).
• DESCRIPTION: A detailed explanation of what the command does.
• OPTIONS: A list of all the flags (like -n, -b, etc.) and what they do.

Navigating the manual:

While inside a manual page, you can use these keys:

• Arrow Keys: Scroll up or down.
• Spacebar: Scroll down one full page at a time.
• /keyword: Search for a specific word (e.g., type /number while in the cat manual to find where it explains line numbering).
• q: Press this to quit the manual and return to your command prompt.

Try it out!
Since you just used cat -n, try typing man cat in your terminal. Look for the -n or --number flag in the description to see how it's officially documented!