Howdy lisachamaineg,
I understand that you're trying to add music to your iPhone in iTunes 12. The process has, indeed, changed somewhat from iTunes 11. Fortunately the article linked below details how to go about doing this in the new version of iTunes.
- Connect your device to your computer.
- Open iTunes. Make sure that you have the latest version.
- Choose the content that you want to add to your device from your iTunes library.
- Drag the content to your iPhone, iPad, or iPod. A panel should appear. Locate your device.
If you're using an iPhone, you can only add music or video from a single iTunes Library.
If you're using an iPad or iPod, you can add music from multiple iTunes Libraries, but video from only one iTunes Library.
Move content from iTunes on your computer to your iPhone, iPad, or iPod touch
https://support.apple.com/en-us/HT201593
Sincerely