How, exactly, does money work?

Where does money come from? Initially it was developed as a means of trade (ie. trading gold coins for some commodity) but these days money is mostly made of inexpensive materials. (A can of soda is not of equal value to a piece of paper) When you get paid at work that money comes from where? Other people who pay for the services that your employer offers or for products your employer produces. But where does that money come from? Other people who do the same thing. Essentially an economy is the moving of money from one person to another. So...money is worth only what people think it's worth. Interesting.

If I'm wrong please correct me, but as I see it economics don't really make sense.