Jupyter Notebook auto-saves itself every 2 minutes. As good practice, you should save it yourself more often by clicking on the floppy icon on the toolbar, or more conveniently by Ctrl + S.

Each project you open on Jupyter is saved as the JSON-based .ipynb notebook format:

The .ipynb notebook is portable across different Jupyter servers. Notebooks can be exported as basic runnable Python script .py, Markdown .md for documentation, and web page format .html for instant display of the flow of your project without having the readers install Jupyter Notebook in advance. It also supports LaTex format and PDF conversion via LaTex upon installation of the dependency Pandoc. If interested, you may check out the installation instructions at http://pandoc.org/installing.html.