So you have a clear understanding about what a synchrnization is and how it differs from a backup and restore, we encourage you to read the overview which follows:

The difference between Backup and Synchronization

You perform a backup when you want to keep a second copy (a backup) of your files. For example, you would backup your files from your computer to an external drive. A backup does not change your original files. If you accidentally delete a file, or make changes you don not want, etc. then you can restore the original file from the backup.

The following graphics illustrate a backup and restore operation:

When synchronizing files you are however copying files between two computers or storage mediums, e.g. your hard disk and a USB memory key. For example, you have a desktop computer and a notebook computer and have copies of the same files on both computers. You may be changing those files either on your desktop or notebook depending on the situation. For example, you may go on a business trip with your notebook and change the files while away. When you return you want to make sure your desktop and notebook have the latest copies of those files. To do this you would synchronize the files.