It might seem really simple, but for all the hate the concept of money gets, it's actually incredibly important to a functioning economy because it solves several fundamental problems for people trying to get what they want, starting with the "double coincidence of wants". In a barter system, both you *and* the person you're hoping to trade with have to want what each other has at the same time. But most of the time, that doesn't happen. Money makes it possible for you to get what you need without needing to have *exactly* what someone else wants.