Instruments can be categorized into four main types: string instruments, woodwind instruments, brass instruments, and percussion instruments. String instruments, like the violin and guitar, produce sound through vibrating strings. Woodwind instruments, such as the flute and clarinet, create sound by air passing through a reed or an opening. Brass instruments, including the trumpet and trombone, generate sound through the vibration of the player's lips in a mouthpiece. Lastly, percussion instruments, like the drum and xylophone, produce sound by being struck, shaken, or scraped. Each type contributes uniquely to music.