Your guests will have things that they need doing, booking in, food made for them, and of course taking the money. The part of the screen flashes up when you need to do something, and you can see the customers getting bored while they are waiting.

At the end of each level, you have the opportunity to spend the cash you have earned, I would recommend getting rocket boots and a chef early on, then you have a choice of all kinds of things which earn extra cash.