Several ways to fix common sync errors that you will experience while using OneDrive.
1. Make sure OneDrive is open
2. Make sure you are logged into OneDrive
3. Pause and unpause syncing
4. Unsync and resync SharePoint document libraries
5. Log out and log back in
6. Reset OneDrive (https://support.microsoft.com/enus/o...)
7. Uninstall and reinstall OneDrive.