What is a coffee Puck? It is easy to see why a coffee puck is called a puck. It resembles a hockey puck. That circular disc of coffee left in the portafilter after your espresso? If all goes well, it should just slide out of the basket when tapped.
If it is moist and soggy, check your tamping.
Each espresso machine has a tamping tool. The flat disc-shaped end of the measuring scoop. It is used to tamp or flatten the coffee in the basket before putting it in. Just the appropriate pressure of tamp. Imagine the surface as a clock face. At 3, 6, 9, and 12 o'clock, tamp. Apply 30-40 pounds of pressure (try practising on the bathroom scales).
When you stop extracting coffee, take the handle out rapidly so the grinds can soak up the water. Soup for you. On the other hand, certain coffee machines always give a souped-up puck. It is all about the coffee.