title_body: What is this tamper/filter thing that came with my moka pot for?
upvoted_answer: OK, I've worked this one out. This little thing is called a reducer.
  
  What you can do is put the reducer into the funnel. It should sit on the indentation half way down. You then put coffee on top of it. This allows you to make less coffee with a larger pot.
  
  However, although I haven't tried it yet, it seems that most people complain that the quality of the coffee reduces (!) significantly. Many complain of a weaker brew. It's probably better to use a smaller pot if you regularly want to make less coffee.