The file contains notebooks with the solutions to previous exercises.
To open these notebooks, open JupyterLab (for example through the Anaconda Navigator).
A jupyterlab window will open in your browser. To open a file, click on the file symbol in the upper left corner (see red circle below). You can then browse through your local file system (to wherever you downloaded the notebook).
Once you open a notebook, there are different cells. You can execute a cell by clicking at it an pressing "Shift Enter".
The cells with text are "Markdown"-cells. If you click at them, the raw markdown text will show. You can convert them back to the compiled form by executing them ("Shift Enter").