While signed in to your Microsoft account, OneNote continually keeps all of your notes in sync. Whenever you work in shared notebooks, OneNote manages your own changes with that of any other authors editing the notebook to make sure that everyone’s work is saved automatically and reliably.
Most of the time, manually syncing your notebooks is not necessary. However, if you want to force an immediate sync of a particular notebook for any reason, do the following:
To the left of the section tabs, click the name of the current notebook.
In the Notebooks list, move the mouse pointer over the name of the notebook you want to sync, and then click the button that appears next to it.
On the menu that appears, click Sync.