Q: how to transfer music from itunes to IPhone...?

A) Stop it already with the huge ugly font. We are not blind, and those of us who may be can enlarge the screen or use a screen reader just fine.

B) Learn to use Google: http://support.apple.com/kb/PH12313

Did you bother looking at the link I posted?

Yes, it is. Apple intentionally hides and obfuscates the file and directory names on the iPod to make it difficult to download music from an iPhone to a Mac iTunes in usable form (going the other way)

Try these steps:

On the new Mac launch iTunes.
From the iTunes menu bar click Store > Authorize This Computer
For your iTunes purchases ...
Connect the iPhone.
From the menu bar again, click File > Transfer Purchases From ..
For non iTunes purchases you may need a utility.

Resource: How can I copy purchased music from iPhone to iTunes library

For iPhone users, iTunes is one of the most powerful tool to transfer data from iTunes to iPhone. However, if you use iTunes to transfer songs to your iPhone which is not synced with this iTunes Library, all the data on this iPhone will be erased. Fortunately, here is a professional iPhone transfer tool to change the situation.

Transfer Music from iTunes to iPhone without Sync

Launch iTunes on your computer and plug into your iPhone to the PC to transfer music from iTunes to iPhone. Click the "File" button and choose to add files or folder from your PC to iTunes library. Click the "Music" icon to sync the audio files. Check the "Sync Music" icon to decide to sync "Entire music library" or "Selected playlists, artists, albums, and genres". If you want to copy the entire music library, check that option and it is done by clicking "Apply". While you want to transmit only certain files, just choose the corresponding option and check the specific groups in the classifications below. After clicking "Apply", the transfer begins.If you want to view the transferred files, click the "Music" button under "On My Device" in the left column.