These all work on the same basic principle, which can be stretched a bit to steamer type "espresso" machines as well. A chamber with water is heated to boiling point; steam pressure forces the water through a "cake" of coffee, extracting the flavour as it goes. Since the manufacturers of these devices do NOT want any exploding boilers, this type of brewer always has a built in, usually "one time only" pressure relief valve. This limits the amount of pressure used in the extraction to well below the espresso "standard" of 9 bar, so you still get a strong coffee, but not a real espresso. However, several million persons of Italian descent brew the base coffee for their morning Café Latte this way, so they can't all be wrong.

The major features of the standard stove-top moka pot can be seen below.

The Top. Screw it on to the base firmly before brewing.The steam formed when you heat the water in the base pushes the coffee up through the tube, and it collects in the top.

 The rubber washer holds the filter screen in place. Take them out for cleaning after you brew.

The Basket sits in the base. Fill it with coffee, level but do not tamp.

The Valve. Never cover it with water!

 The Base. Fill it with water up to the bottom of the valve.

  Coffee for the Espresso pot should be coarser than espresso grind but finer than for filter grind, although at a pinch a decent filter grind is O.K. The basic steps for brewing can be broken down as follows:

1) Fill the base with water to just under valve.
2) Fill the basket with coffee and level it off, so it's reasonably firmly packed. Do not tamp.
3) Insert basket in base.
4) Screw the top onto the base, tightly enough to get a good seal with the rubber ring.
5) Place on medium heat source and watch while it brews, do NOT wander away.
6) When coffee begins to flow steadily into the top (or out of the spout(s)) turn off the heat, but leave the pot on the stove.
7) The residual heat should be sufficient to complete the brewing. Do not wait until all the coffee is brewed to turn off the heat, as this will give you a bitter, over extracted coffee. Remember that a single "tasse" is 30ml.
8) Wait until cool, disassemble and clean.

For a true Italian Café Latte, heat some milk in a small pot until it just starts to boil at the edges of the pot, then pour into a cup which is already half filled with your coffee.