How to add a OneNote notebook to a Team

Start by selecting the desired Team from the list:

Select the Add button from the top once the Team is open.  It looks like a plus symbol (+):

Select OneNote from the list of apps to choose from:

From here you can choose to add a new notebook or select the default notebook.  The recommended choice is the default notebook:

This will add the notebook as a tab to select at the top of the Team when it is opened: