Syncing is EndNote's method of copying your desktop library to EndNote's own online platform. EndNote will automatically copy any changes you make to your desktop library into your online library version in real-time. If you are using the EndNote Online version of your library, next time you open your desktop library EndNote will add your changes made in EndNote Online.
Once the online version of your library is created from one desktop library, a second desktop library on a different computer or device can also be synced.

Sharing your EndNote library for collaborative research, use EndNote's desktop sharing method or via the EndNote Online platform. 
Do Not try to access and share your EndNote library with collaborators on cloud servers. Your EndNote library will become corrupted.