A charge card is like a magic card that lets you buy things without using actual money. But it's not really magic because you have to pay back the money you spent later on.
Imagine you have a piggy bank with your allowance money in it. When you want to buy something, you take out some money from your piggy bank and give it to the person selling the thing you want. But with a charge card, you don't have to take out money from your piggy bank. Instead, you swipe the card and the charge card company pays for the thing you want to buy.
Then, at the end of the month, the charge card company sends you a bill for all the things you bought using the card. You have to pay back the charge card company the exact amount you spent using the card. It's like borrowing some money from the charge card company and promising to pay it back every month.
But, if you don't pay back the charge card company the exact amount you spent, they can charge you extra money which is called interest. So, it's important to always pay back the charge card company on time and in full so you don't have to pay extra money.