1) First, import music (songs) into the iTunes library.

Open itunes and click "File" in the upper left corner, then click "Add File to Library" (this refers to a single file) or "Add Folder to Library" (this refers to a single file) on the drop-down menu. refers to the entire folder). If you want to selectively add it later, use the first option. Open the folder where the songs are stored on your computer and selectively click on it and confirm.

Then check whether the song is in the iTunes library: click "Music" under the library on the upper left and see if your song is included in the expanded interface on the right. Yes! Like this The conditions for transferring to the device are met; if

you want to put all the songs in the entire folder into the iTunes library, then select the second option. No matter which one you choose, after confirmation, it will be in the iTunes database.

2) Transfer music (songs) to the mobile phone

Click "Your iPhone" under "Devices" in the iTunes library, and then open It is an iPhone interface, with summary, information, applications, music, movies, TV shows and photos.

You just click on "Music" on the top, and then click "Sync" on the lower right. After that, you still need to click "File" on the iTunes interface and select "Sync your iPhone" from the drop-down menu, so that your music will be on your iPhone 4S.