Connect the phone to your Mac with the cable. Launch iTunes. Unlock the phone (enter your passcode) if necessary. Since this is your first time connecting the phone to the Mac, you will get a pop up message asking if you want to Trust This Computer. Click on Trust.
About the 'Trust This Computer' alert on your iPhone, iPad, or iPod touch - Apple Support
After you trust the computer, select your phone from the device icon at the top in the iTunes side bar. You should get a prompt to set the iPhone up as new or restore the backup. You want to restore the backup. Select the backup that you want to restore and then restore it.
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
After the backup restores, sync your phone with iTunes. If you synced the iPhone 6 with iTunes in the past which I assumed that you did, your sync settings should already be set to sync all of the music that you imported from CD’s.
If you eject the phone after restoring the backup, Leave your phone connected to WiFi in order to download all of your apps.
If for some reason all of the music or other content that you wanted to sync didn’t come over, just go through each section and make sure that the content that you want to sync is selected to sync and then sync again.