Banks are used as stores to keep and protect money, and they use this money which they know we gaurd jealousy to trade and make profit while at it. So when individuals deposit money they use some part of the deposits to trade and make profit while keep ur money intact.
It is true that banks can use money from accounts in order to trade with it but they can not do this always because it is illegal to use our money if we want to keep it safe in our account. The visible way of making money is in terms of transaction costs and interest rates etc, banks cut transaction costs on different currencies have different rates so this is the visible way of making money.