The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
The number 0-11 are distributed on a game board with 64 fields. You choose horizontally, the iPhone (your opponent) chooses vertically. Blue numbers increase your score, red numbers decrease it. The game finishes when no more fields are available. Sounds easy? Try it!