Selling a song for free on online stores and streaming services like iTunes is not possible.

If a song is available for free download on iTunes, it's because the iTunes editorial team has made that decision.

However, if you want to make your music available for free to the public, you can try Bandcamp. On the other hand, if you want to give your music away to specific people like radio stations, DJs, or friends, you can email them your MP3s or WAV files or use a file hosting service like Dropbox to share a link. Additionally, you can purchase your own songs on iTunes and gift them to others by opening iTunes on your Mac or PC, selecting the sub-menu to the right of the price, and clicking "gift this song." For more detailed instructions, see this article.