I have no idea why 3 "extra" character, do you?
On the upper left on the keys, in red, is the character set known as "Bopomofo", or the "National Alphabet". This is an alternative way to express Chinese phonetically, instead of using our Roman alphabet to type in Pinyin.
The lower right of the keys contains the characters assigned to the keys when typing text using the DaYi input method. That is a popular and efficient commercial input method for Chinese which allows typing characters based on their appearance.
The lower left of the keys contains the characters assigned to the keys when typing text using the Zhuyin Fuhao input method. This is another method for typing in characters based on how they look; it's the most common one which has been around for quite some time.