There are several factors leading to why people can't use a credit card. Credit problems, etc. You name it.
No credit card means it's impossible to buy online... unless it's the online Apple Store, which allows cash payments through a process.
Now you may be asking, "doesn't Apple sell online the same things they sell in stores?"
The answer is no. There are lots of exclusive items, such as Herschel backpacks only available online.
To get started, you need to take a trip to your local or nearest Apple store.
Step 1: Go to the Apple Physical Store and Buy an Apple Store Gift Card
These gift cards are lesser known than the iTunes/Books/AppStore cards, but they exist. If you ask at your local Apple store, you can buy one for any amount. Usually, what you are going for is the price of what you want to buy. What you pay is what the card's balance is. Once you've got the card, you can spend it in store, or because I'm teaching you how to do this, go home and spend it (up to 8 cards in a transaction) online.
Step 2: Redeem and Checkout
Once everything is in your cart, go to the checkout screen. in that payment screen, select the Apple Store Gift Card tab. To redeem, simply follow the on screen instructions. Place the order, and you've successfully completed an online Apple Store transaction without using any credit cards and just pure cash.