A stethoscope is primarily used to listen to sounds within the chest, particularly heart and lung sounds. The instrument amplifies the internal sounds of the body, allowing healthcare professionals to assess vital signs and diagnose conditions. When placed on the chest, the stethoscope can pick up sounds like the heartbeat, breath sounds, and any abnormal noises that may indicate issues such as heart murmurs or lung congestion. Furthermore, stethoscopes can also be used in other areas, like the abdomen, to listen for bowel sounds, providing a comprehensive view of a patient's health.