Follow the below steps to Sync iPhone, iPad, or iPod to iTunes.
How to Transfer Music from iTunes to iPhone, iPad, or iPod
Step 1. Download the iTunes from here https://www.apple.com/in/itunes/download/ and install in your PC
Step 2. Once the iTunes get install in your PC open the iTunes app and click on sign in to the iTunes store
Step 3. Login with your register apple id
Step 4. After successfully login click on the Store button
Step 5. Click on Purchase to get music from iTunes to iPhone
Step 6. Click on the button marked in the image and your song will get download
Step 7. Your downloaded song will be available in your pc at the place Music\iTunes\iTunes Media\Download
Step 8. To transfer this in your iPhone connect your iPhone with your computer via USB
Step 9. Now click on Music where you can check available song in your iPhone
Step 10. Go the download folder and copy the song
Step 11. Paste the song in iTunes Music
Step 12. That’s how you can transfer iTunes to iPhone music.