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.
From Ronald Bell:
Mandarin Word of the Day is a Mandarin study tool designed to help you learn a new word every day. Learning a new word every day is a simple and fun way to improve your language skills without becoming frustrated or overwhelmed. Missed yesterday's word? Want to take a sneak peek at what's going to come tomorrow? Use the Previous/Next buttons to freely navigate through the full list. Be careful of other study apps which may require a network connection in order to function. This app requires no network connection, allowing you to study anywhere. Perfect for travelers who may not have connectivity at all times.