Exchanges work in a very simple way. Here's an example:
I want to buy a lollipop in this price. (say $1) then a dude wants to sell his lollipop for $1. The exchange will act as a medium between us to process the transaction and in return, the exchange will charge fees as the "facilitator" of the deal that occurred between us.

Hope that that isn't hard to understand.

exactly the way he said it.