Q: how do I transfer music from my mac book air in iTunes to my iPhone 6

Sync your iPhone, iPad, and iPod with iTunes using USB - Apple Support - https://support.apple.com/en-us/HT201253 - detailed example: https://discussions.apple.com/message/18860187#18860187

Sync your iPhone, iPad and iPod touch with iTunes using Wi-Fi - Apple Support - https://support.apple.com/en-us/HT203075

I just found one of the software which can be helpful to transfer music from MacBook Air to iPhone 6. It's called, "iTools". And it's free. I just transferred an album of music to the iPhone with it. The problem is, the mp3 tag information did not transfer along with. So the artist names do not show, and the songs don't get properly categorized. If this exists, there must be something better out there that will transfer both the songs and their id3 tags from Mac to iPhone.

1) There should be no need for special software to transfer to a phone. iTunes can do the syncing and is specifically designed to do that.  I would be hesitant to use third party software for this purpose.

2) Tag information is embedded in mp3s.  If the tool is not transferring the tags then it must be specifically deleting them, modifying your mp3 files.  It should not be doing this.

there must be something better out there that will transfer both the songs and their id3 tags from Mac to iPhone.

iTunes

Really, all you have to do is make sure your software and iTunes is up to date on your Macbook Air. If everything's up to date, do the following in this order: Get on iTunes, Once you're on iTunes look at the top of your screen and click iTunes, click on preferences, click on general. Now, once you're on general on preferences on itunes, there should be 2 checkboxes under a text box. Click onto the tiny square to check the 2nd option that should say 'iCloud Music Library.' Once you do that, check on your phone and your music from your Mac should be there! Pictures below just in case!