How come my music off of my computer is not able to be put on my iphone 4s?

My phone is synced to the computer I'm currently using and everything so I don't understand why I can't just drag the music to my device.am I going to have to end up restoring my iPhone or what should I do?

Q: how come my music off of my computer is not able to be put on my iphone 4s?
A: You don't know what you're doing because you can't be bothered to read the manual for your product.

Refer your user manual.

If you don't have the music in iTunes, you can't put it on your iPhone.iTunes uses MP4 and you can easily convert it, but it might take a but of time to change it all into iTunes files.