Q: i purchased ipad mini 2 but it is asking my billing information even for a free apple user guide.what should i do

Unless you use the instructions on this page when creating a new account : Create an iTunes Store, App Store, or iBooks Store account without a credit card or other payment method - Apple Suppor…

then you will need to enter payment details before the account can be used to download anything (including free items) - you should be able to remove your payment details after entering them.