You must be trying to fill out a form on the internet, aren't you? That would explain the postal code error you're getting in your question #3.
Do you know what furigana is? Japanese names are written in Chinese characters, as you may well know. The problem is that sometimes it's hard to read a name just by looking at the Chinese characters, so the furigana spot is the place where they write how to read their names. Same goes for addresses.
BTW, mail address refers to your email address.