A bouzouki is played by holding it like a guitar and plucking or strumming the strings with a plectrum. The strings are arranged in four pairs (each pair tuned to the same note) so when you hit them together you get a thicker, brighter sound than a guitar. Skilled players can play very fast melodies, like singing in metal.
Bouzouki music almost always makes you want to move. There is a famous Greek dance called the syrtaki that goes with it - dancers hold each other's shoulders in a long line and start out slowly. As the music speeds up, the dancers go faster too, kicking and crouching in time. By the end, everyone is laughing and out of breath.
You'll hear bouzouki in tavernas - small family-run Greek restaurants where people eat, drink and listen to music in the evening. Sometimes there's a live band; sometimes just one person on a bouzouki and a singer. Diners often join in singing along, or even get up to dance between courses.
Even though it is now seen as the most Greek of instruments, the bouzouki actually came to Greece about 100 years ago from neighbouring countries to the east. Musicians in Athens fell in love with the sound and made it their own. That's a nice reminder that culture moves around - the most Greek of instruments has roots all over the place.