if you play D4 note near the violin, the body of the violin will vibration with it, as Resonance
(Frequencies at which the response amplitude is a relative maximum are known as the system's resonant frequencies or resonance frequencies)
Buying Guide
Frequent change ones:
string: like guitar, it can be super cheap
bow: the wood stick with horse hair, it can be cheap and expensive as well, just buy cheap popular one
Bow size: the full/adult size is 4/4 scale, at length of 74cm. there is mini version of bows for the mini version of violins, which are for kids. the scale is measured like toy model car.
rosin: the solid liquid to smooth the hair of bow, super cheap