How to get music to my iphone from my itunes library?

I upgraded to the new itunes and i'm having difficulties getting the itunes library music to my phone

I'm guessing by the new iTunes, you mean the one that was just released, iTunes 11? And by iPhone, you most likely have iOS 5 or 6 running? If you don't, be sure to update to that in the Settings on your phone. Once you know your software, on your phone, open Settings, tap iCloud, then tap Storage and Backup. Then scroll down to iCloud Backup and turn it off temporarily. Once iCloud Backup is off, connect your iPhone directly to your computer via USB and then sync music. On the top right, you should see the name of your device. Click on that and then select the music tab. Select individual song/playlists/etc or choose everything. Then click apply and sync. Make sure you have enough space on your iPhone and your computer. Once you have synced music, open your phone, check to see if it's there, and then you can either turn on iCloud Backup or turn on Music in your automatic downloads. Then whatever you download on your computer or phone connected to the same Apple Account will automatically sync.iCloud Backup just automatically backs up everything to your computer when signed in and connected to power and Wi-Fi. If it's off, then iTunes will back it up when open and automatic downloads will occur anywhere, even with Cellular Data if enabled. Hope this helped!