If you're seeing the error 'jupyter' is not recognized as an internal or external command', it's likely Jupyter isn't installed or isn't in your PATH. Try pip install jupyter, then verify with pip show jupyter. If it's installed but still not working, add its installation path to your system's PATH variables. Full step-by-step guide here: https://coderlegion.com/302/how-to-fix-jupyter-is-not-recognized-as-an-internal-or-external-command.