Besides, your operation is incorrect. You need to download something to your mobile phone. It should be in the upper right corner, that is, you plug in the name of the device next to the itunes store, click, expand the device, select the software and audio you want, and then click Sync in the lower right corner.

Synchronization means that the data in the device and the computer are consistent. If you sync directly, your device, other software and music will be erased, except the content in itunes.