I am new in app store.. when trying to download any app it displaying an alert msg" this apple id has not yet been used in itunes stores" review your account information.... so it is neccessary & safe to enter all our credit or debit card information?
By default, Apple requires some kind of billing information in order to use an Apple ID in the AppStore.
You can work around this by "buying" a free app first, then you will have the option not to add any payment method so you can go with gift cards only.
But normally (unless your device is infected which is unlikely), it's safe to add this information (as safe as it can be)