Currently only US users can purchase items from the store but in the future they would make it available users all around the world (hopefully). Currently they may not have a lot of apps but for a start it is said that they have around 4000 apps available.
Through their service now you can securely download (purchase) movies, audio track, books, games, etc directly to your android phone. According to them, every day you'll be given the change to free download an app that is popular and non-free!. Surely, Amazon knows how to sell "things" without a doubt ;-).