How do I listen to mp3 audio files on my iPhone 4s?

Are you crazy? In iTunes-speak, "Sync" means "erase!" Sync is safe only If your iTunes library and iPhone can have the exact same contents. But if you have had any complications at all, using Sync endangers all your files.

• I had to rebuild my iTunes library after switching to a new computer, so I had hundreds of tracks on my iPod that weren't in my library. Using Sync erased all of them!
• I have multiple old devices. I put music on the iPod, career-related podcasts on an iPhone 3, books on tape on an iPod mini (which has comparatively little memory, and so on. The iTunes Library does not remember which tracks go on which device. Using Sync destroys that organization.
• I have thousands of tracks in iTunes on my computer. Even if I used only one device (e.g., my iPhone 5), only a fraction of them will fit on the device.
• If I want to transfer a single track to my iPhone, using Sync can waste a huge chunk of my time by indiscriminately deleting and transferring an entire library.

Even Microsoft couldn't have come up with a file-organizing system worse than iTunes. It's not so great for finding what you want in the iTunes Store, either. And Sync can burn a lot of time and money that you'll never get back.

You can easly found them in Music on you iphone because transferred music is placed in it ...

I think ...

Connect your phone to your computer. Click on its name in iTunes. Click on the Music tab. Make sure the songs are checked, unless Entire music library is checked. Click Sync.

You're welcome! Happy holidays.

I also have purchased and downloaded an mp3 audio file (not from itunes) onto my macbook air. I was able to transfer it to my itunes library. I now want to listen to it on my iphone 4s. How do I do this? If i go to the itunes store application, i can see my "purchase" . I emailed the mp3 (it went to a downloader automatically). I couldn't open it in email to listen to it on my iphone 4s. So I purchased idownloader pro". still cannot listen to them on my phone. Isn't there a way to transfer them without physically connecting the mac to my iphone? afraid to do this as I screwed up my files, etc doing this in the past!! Any suggestions??? Thank you!!

You must import the mp3 into iTunes on your computer, then sync it with your iPhone over a USB cable or WiFi. There should be no problem syncing with your Mac, unless you tried to sync with more than one computer; an iPhone can only sync with one computer at a time.