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Explanations on credit cards in Canada
I think it's worth pointing out explicitly that the biggest difference between a credit card (US/Canada) and a debit card (like your French carte de crédit) is that with a credit card, it's entirely possible to not pay the bill or to pay only the "minimum payment" when asked. This results in you owing significantly more money due to interest, which can snowball into higher and higher levels of debt, and end up getting rapidly out of control. This is the reason why you should ALWAYS pay off the ENTIRE balance every month, as attested to in the other answers; it's not uncommon to find people in the US with thousands of dollars of debt they can't pay off from misuse of credit cards.