On debit cards, the money goes straight out of your account to the payee, so it's harder to get your money back.
On credit cards, the *credit card company* pays the payee. They then want you to recompense them. If you contest what the payee charged or if you have a dispute over what you received, you tell the credit card company and *they* foot the bill. That way you're protected. Incidentally, Amex might work in the States but many/most shops in the UK don't accept it because Amex charge too much - you need Mastercard or Visa if you're travelling in the UK and Europe.
As regards interest on credit cards, you only pay interest if you can't make the repayments each month. If you don't pay it back, you pay interest.
I often wonder whether all those people running up vast card bills believe the Tooth Fairy will magically bring them more money. If the issue was getting into debt for essential food and rent then I would have some sympathy, but most of them are spending the money on clothes and other luxuries, and I have zero sympathy for that.