I already wrote some posts about OneDrive and its new functionalities available by default to all Windows 10 users, and maybe you could be interested in some of them (How to configure OneDrive in Windows 10; Windows 10 Fall Creator: nuova funzionalità di Files on-demand (ex placeholder) in OneDrive [anche per OneDrive for Business e documenti su SharePoint]). In this post I am going to provide a new tip!
Usually the OneDrive agent is configured to start at the startup of the O.S. but possibly you could uncheck this feature from the Settings tag of the setting section, available right-clicking on the toolbar OneDrive icon, because you do not need to have it running in the background every time.
Moreover, it may happen that agent crashes, possibly because of authentication problems that may happen if you are using your PC behind a firewall: in this case an alert popup window appears and then the OneDrive icon will disappear from the taskbar because that agent died.
In these cases you would want to start that OneDrive agent manually.
If you try to find how to do searching OneDrive with the Cortana search feature, you may not find much help because it only gives some links to the app installer, possibly older than the version you have, … but no way to start the OneDrive agent.
Clicking on the found result, simply start the installation of an old version of the OneDrive app:
Instead, what you have to do is to run the following instructions from the Run [IT: Esegui] window that can be opened right-clicking on the Windows icon of the toolbar and choosing the Run menu item (or contemporary press Windows + R):