Contact a digital music distribution service like TuneCore or CD Baby. These companies will make it possible for you to sell music on the iTunes store.
Submit your music and artwork to the music distribution service of your choice.
Submit your banking account information to the music distribution service. This will make it possible for you to transfer funds from the music you sell to your bank account.
Pay the necessary fee to the music distribution service. For example, TuneCore will charge you an annual fee to keep make your music available on sites like iTunes and Amazon, while you get to keep all of the profits.
Promote your music once it is available on iTunes. Spread the word about your music in blogspots and forums and on social networking sites.