When you deposit money in your Bank they can lend them to someone else, up even to 90% making profit from it.

The person that borrowed money now has money in his bank account, and imagine is a different bank, 90% of those money can be lend to someone else.. and so on.

Banks have obligation to maintain just a fraction of the money you put in your bank account. It's a huge rabbit hole when you understand there's no money in First place, it's all debt.