How to buy an app for iphone?

I just got an iPhone and I was buying this app when it asked me about payment through credit debit or none etc. What happens after I press credit, I enter my number and that's it? And if I press none does it go to my phone bill?

Put all of your debit card/credit card details when it asks you to do it it then App Store. It will take it from the card (bank) not the phone bill.

It debits from your bank.

You cna just put your credit card in on itunes, then when you put your password in it will automatically credit.