Important: Keep in mind that you always need both files! Never remove one of these files, or you won't be able to use it anymore. When you want to rename the database: do this on both the files.
Tip: store the files in the same (sub)directory and if you want to move the library to another location: Sort by name first and move both files!
Never use EndNote libraries in cloud-syncing folders. This includes folders such as OneDrive, SurfDrive, Dropbox, Google Drive or iCloud. This can cause data corruption and eventually loss of data.
EndNote suggest using EndNote Sync if you want your references available on more than one computer. Another option for sharing references is making a compressed library: this will create one .enlx file in a zipped format. You can share this library in a folder like SurfDrive, but make sure it will be downloaded on the computer itself.