From Mac Guides
The iTunes Store (originally the iTunes Music Store) is a multimedia download service operated by Apple. Using a proprietary Internet browser built into the iTunes software since version 4.0, it offers music tracks, movies, TV shows and iPod games for sale, and movies for rent. Other services are provided free of charge, such as movie trailers and a podcast directory.
Currently, the store is available in Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, and the United States. A credit card with a billing address in one of these countries is needed to purchase songs from iTMS, but the free services and song previews are generally available to all.
On February 2010, Apple has sold 10 billion songs, more than twice that of two years ago. 125 million TV shows and 7 million movies have also been sold.
Apple announced Video sales through iTunes on October 12th, 2005. The announcement came alongside the release of video-capable iPods. At launch, Apple offered over 2000 music videos, 5 television shows and 6 Pixar animated shorts. Each video cost $1.99 (US) each.
On September 12, 2006, coinciding with the release of iTunes 7, the iTunes Store began selling full length Disney affiliated movies , and now also offers movies from Paramount.
iTunes now offers TV content from ABC, ABC Family, Comedy Central, Disney Channel, ESPN/ABC Sports, MTV, NBC, Nickelodeon, Sci Fi, Showtime, SOAPnet, The N & USA networks. Television shows offered include ABC's Lost, Desperate Housewives, and Night Stalker; Disney Channel's The Suite Life of Zack and Cody and That's So Raven (these 5 constitute the original offering); USA's Monk; NBC's Law and Order, The Office, Surface, The Tonight Show with Jay Leno, Late Night with Conan O'Brien and "vintage" shows Alfred Hitchcock Presents, Dragnet, Adam-12, and Knight Rider; Sci Fi's Battlestar Galactica and Battlestar Galactica: The Miniseries.
There are video podcasts that are currently free of charge. These are not necessarily formatted for use on a 5G iPod.
At Macworld San Francisco 2008, iTunes Movie Rentals were announced, with content available from Touchstone, Miramax, MGM, Lionsgate, Newline, Fox, Warner Brothers, Disney, Paramount, Universal and Sony. Library titles are available for $2.99 USD while new releases cost $3.99. Purchasers have 30 days to start watching a rental and 24 hours after that to finish it.
Most purchased tracks include digital rights management information, called FairPlay by Apple. A computer must be registered with Apple by the track purchaser before the tracks can play. Currently, each user is allowed to have up to five registered computers. Any number of iPods may also be used (these do not need to be registered), and each playlist containing protected tracks may be burned to CDs a maximum of seven times (with no limit on burning individual tracks).
In April 2007, Apple and EMI announced that EMI's music would be available in a DRM-free version at twice the sound quality for $1.29 USD per track, in addition to the traditional DRM tracks for $0.99. Albums and music videos were made available without DRM with no change in price. 
Apple only allows the purchaser to download a track once, so it is very important to make backup copies. If you lose a song you purchased, you will need to purchase the song again. More information is available at at Apple.
Individuals cannot sell tracks directly through iTMS, Apple will deal only with record labels and distributors. Unsigned artists can get into the store through independent distribution services like CD Baby.
An alternative way to make material available is through podcasting, which operates independently of iTunes. Apple will list podcasts in the iTunes Store if the downloads meet their conditions. Podcasters should also consider adding Apple-specific tags to their RSS feeds so that their iTMS entries show up properly.