If you want to synchronize faster, or you don't have wifi, just connect your phone to your computer through a data cable, open itunes, press the icon on your phone, and click Sync in the lower right corner (sometimes the application will be displayed).
Note: Please download itunes(MAC)(MAC) before synchronizing (MAC will come with it). Check the content you want to synchronize in the mobile phone page. If the contents of the mobile phone and the itunes database are inconsistent, then itunes will delete something different, so you should back it up first. If you don't even know the synchronization, then don't play iphone, which means that if you want to play iphone well, you must master these basic knowledge by yourself and can't rely on others.