Espresso machines use hot water under high pressure to pass through finely grounded coffee. Coffee prepared by this method will be very bold and with crema, a thin foam layer on the surface, which plays an important role in creating the coffee aroma.
There are two types of espresso machines: automatic and manual. Automatic espresso machines only requiring filling the machine with coffee beans, and pressing a button. This produces a mediocre cup of espresso. However, if you want a standard espresso, you should use a manual machine.
A well pulled shot of espresso should have crema, which is a light brown cream on the surface. If you want a thicker layer of crema, you should make espresso as soon as the coffee is grinded. Freshly ground coffee makes the best cup.