The bottom line is, iTunes won't deal directly with individual artists. Not to worry, though -- the digital age has indeed democratized access for individual artists to the newest distribution channel. You can sign up with any one of a number of distribution intermediaries who can get your music on iTunes, as well as other digital music stores.
Before you sign up with a distribution service, you want to get your music in shape. First task is to have your recording mastered, which means you (or a professional) has optimized your digital music file to sound its best. As part of this process, you'll make decisions like which music files you really want to make publically available. You can just release a single or an entire album.
Once you know what you want to upload, you'll need both a UPC (universal price code) and ISRC (international standard recording code). Most of the distribution services will arrange these codes for you; some bill an additional fee for this, some don't.
Pricing models used by the different services vary widely. It can be a monthly subscription with no royalties to the service; flat fee per track or album with an additional royalty percentage going to the service; or a low flat set-up fee with additional per track/album fees and low royalty percentage. Some services will bill a range of flat fees depending on the number of digital music stores where you want your music. The two most important points to understand about pricing are a) the cost to enter the market through these services is quite low, so there are no barriers anymore to getting your music out there; and b) the pricing model that makes sense for you will depend on the volume you want to post.
The best news: With most services, you'll retain all the rights to your music.