Paying can be a confusing experience. If you are wanting just a coffee or Panini from a café you have two choices. One- look at what's on offer in the display case, find a table and sit down to wait for the waiter and tell him, at the end just ask him for the 'conto' or the bill. Two- check out the display case, make your way to the 'cassa', pay for your choices and then take the receipt over to the serving counter. It's all about the Italian tax system, but in some ways it makes sense that the food servers are not spending time working out change etc.