How to buy an app on the apple store?

Every time I try and buy an app a little nonification message pops up saying " payment information required " When I press continue it takes me to a page called " Account settings " And it names a bunch of payment types like Visa, Mastercard, Amex, etc Im supposed to choose one but I actually want to pay with paypal but if i cant, I COULD pay with one of the cards but it asks for the card information like its number & security code ( As expected ) but when I asked my friend (who has owned an Iphone for many years) he told me he has never has or had to go through all that when he buys an app so I thought it was kinda fishy but in conclusion, my questions are Do i fill out the card information without worry? If I DO fill out the card information will I be able to purchase the app from there? & is it possible to just pay with paypal?

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