To transfer music from PC or Mac to iPhone you will need an iTunes program.
First launch iTunes program and create there a playlist in this iTunes program. Next connect iPhone to your computer by cable and you will see your music.
The iTunes is the easiest way to transfer music from PC to iPhone. But you need to get to know it first. After that it can be very easy to transfer music from PC to iPhone.
So remember:
1. Download iTunes.
2. Create playlist in iTunes.
3. Connect iPhone to computer.
4. Transfer palylist to iPhone.
5. Click sync, done or apply
And that should be it in the topic of how to copy music to your iPhone. There are many other ways to move music to your iPhone. But this one is one of the easiest ones.