A brass instrument is a musical instrument that you play by blowing through a mouthpiece to change the pitch, or note.
Brass players use their breath to produce sound. Instead of blowing into a reed, they vibrate their lips by buzzing them against a metal cup-shaped mouthpiece. The mouthpiece helps to amplify the buzzing, which creates the sound. Most brass instruments have valves attached to their long pipes; the valves look like buttons. Pressing on the valves makes them open and close different parts of the pipe.