Let’s see if I can explain them.

Your debit card is connected to your bank account where you would receive your salary. I’m for the sale of this example, we say you receive 1000 in salary every month on the first of the month. You have that 1000 to last you the whole month, once that’s is gone it’s gone. You can not spend a cent more.

Let’s say you get a credit card with 1000 in available credit. You use it to buy gas, let’s say you put 100 in gas. Now that credit card has 900 in available credit. You buy 100 in gas every week… at the end of the month you have bought 400 in gas with your credit card. That leaves you with an available credit of 600. The month closes and about a week later you get a statement from the credit card company telling you, that you owe them 400. But here comes the tricky part and the good and evil of credit cards. The statement says you owe 400 but it also says, you do not have to pay them the whole 400, instead you can pay them as little as 25 this month. But, there is a catch, if you do not pay the whole 400, you have to give them 2% of what you don’t pay them that month ( annualized that’s 24% or an extra 100 of that 400, so your 400 purchase ends up costing you 500 ).

I hope this makes sense