The function of a network switch is to connect devices within a local area network (LAN) and manage data traffic between them. It operates at the data link layer (Layer 2) of the OSI model, forwarding data frames based on the destination MAC addresses. This reduces network congestion by ensuring that data packets are sent only to the intended devices rather than broadcasting to all connected devices. Switches enable efficient communication, enhance security through segmentation, and support multiple simultaneous connections, crucial for maintaining network performance in busy environments.