As with all pneumatic instruments, the sound is produced by blowing air through the lips, creating a sound that travels through the tube, provoking standing wave vibrations in the column of air inside the trumpet. Players can choose notes in a variety of overtones or melodies by varying the lip aperture and pressure. The horn has a rounded rim, which allows the lips to vibrate quite comfortably. Directly behind the rim is a horn box that pushes air into a much smaller hole that is adjusted to match the duct diameter of the horn. The dimensions of the above components alter the tone or quality of the sound produced, and make use of the horn comfortable. In general, the larger the horn box, the better the tone and sound.
Modern horns have three (or four) piston valves, each of which increases the length of the tube when joined, thereby reducing the pitch of the pitched note. The first valve reduces by 1 arc (2 semi-arcs), the second valve reduces by 1 arc (3 half arcs), and the third reduces by 1 1/2 arcs (3 arcs). With the fourth valve, in some trumpets / flutes, it usually reduces 4 complete arcs (5 semitones). Individually or in combination pressing the valves at the same time allows the trumpet to play all twelve notes of classical music.
See more at: Life is something like a Trumpet poster