Command Prompt is a command line interpreter application available in most Windows operating systems.
Command Prompt is officially called Windows Command Processor but is also sometimes called the command shell or by its file name cmd.exe.
Command Prompt is used to execute entered commands.
Command Prompt is most commonly used to execute batch files, perform advanced administrative functions, and troubleshoot and solve certain kinds of Windows issues.
How To Access Command Prompt:
Command Prompt can be accessed via the Command Prompt shortcut located in the Start Menu or on the Apps screen, depending on what version of Windows you have.
See How Do I Open Command Prompt? for more detailed help if you need it.
Another way to access Command Prompt is via the cmd run command but using the shortcut is probably faster.
Important: Many commands can only be executed if Command Prompt is being run as an administrator. See How To Open an Elevated Command Prompt for more details.
How To Use Command Prompt:
To use Command Prompt, you must enter a valid command along with any optional parameters. Command Prompt then executes the command as entered and performs whatever task or function it's designed to perform in Windows.
A large number of commands exist in Command Prompt but their availability differs from operating system to operating system. See my table of Command Availability Across Microsoft Operating Systems for a quick comparison.
You might also want to see my List of Command Prompt Commands which is essentially the same as the table but with descriptions of each command and information about when it first appeared or why it was retired.
I also keep operating system specific lists of commands as well:
List of Windows 8 Commands
List of Windows 7 Commands
List of Windows Vista Commands
List of Windows XP Commands