The espresso machine was first invented in 1884 by Angelo Moriondo, a Turinese restaurant operator. It was to satisfy the growing demand of his customers that he had the idea of making a machine serve coffee more quickly.
Since then, the machines have obviously evolved a lot but the espresso is and will always be obtained by percolation under high pressure quickly passing hot water pressurized (9 bars).
Espresso is an art that requires a lot of practice and trial and error. This video will help you lay the basics of espresso, but each setting must be tailored to your machine, your coffee and your tastes.