How to get your iPhone to sync?

I have an iPhone 4S and it won't sync to my computer. I tried to, but some of the music I have on my iPhone won't sync to my computer.Am I doing something wrong?

Did you purchase them on your iPhone? Then transfer your purchases to your computer.

Here: http://support.apple.com/.../kb/HT1848

The same thing happened to me and i wasn't able to restore my music i had to restore my phone to at least get the new music from my computer to sync

You can have a try the iPhone Music Transfer, which can sync all your iPhone content to your computer, how it works, you can learn the following guide.

Try PC Suite for iPhone
http://download.pandaapp.com/ios-iphone-app/91-pc-suite-for-iphone-2.9.72.360-id22578.html