jupyterlab/docs/source/getting_started/starting.md

Starting JupyterLab

Start JupyterLab using:

jupyter lab

JupyterLab will open automatically in your browser. You may also access JupyterLab by entering the notebook server's URL (http://localhost:8888) into the browser.

Because JupyterLab is a server extension of the classic Jupyter Notebook server, you can also use JupyterLab by starting the classic Jupyter Noteboook jupyter notebook and visiting the /lab URL (http://localhost:8888/lab) rather than /tree (http://localhost:8888/tree).

Anytime you are using JupyterLab, the classic Jupyter Notebook is still available at this /tree URL (http://localhost:8888/tree), which makes it easy to go back and forth if needed.

JupyterLab has the same security model as the classic Jupyter Notebook; for more information see the security section of the classic Notebook's documentation.