Two. Credit cards are mainly used for overdraft consumption, and generally have an interest-free period of 20 to 56 days. As long as they pay back the money on the repayment date notified, they will not charge interest. If you don't pay it back within the time limit, you should not only charge interest, but also record your credit.
Three. As for how much money you can borrow, it depends on the credit line given to you by the bank. I suggest that you don't borrow cash by credit card, because there is a charge for withdrawing cash, and the interest is higher than ordinary loans. You can kill two birds with one stone by letting your friend swipe your card and then give you the cash.
Four. When your credit line runs out, how much do you have to pay back before you can use it?