how can i get postcode for apple id please answer

Your saying 'postcode' rather than 'zip code' suggests you are in the UK. If you are, you can get the postcode for your address at https://www.royalmail.com/find-a-postcode

The postcode is tied to your billing address that you are putting on the account. If you don't think you have them where you live but you are being prompted to enter one : http://www.apple.com/support/itunes/ww

What do you mean?