In the normal context of networking, a switch is an OSI Layer 2 device. It operates at the Data Link layer. A switch is just a bridge with more than two ports. The switch then determines which interface the destination address can be reached through. It then establishes a hardware connection to that interface and the frame proceeds to its destination.
Switches prevent frame collisions from occuring.
Their use reduces the size of an Ethernet Collision Domain and extends the size of an Ethernet network. Switches utilize one of three methods to examine frames. It then examines the MAC address. It compares the MAC address against an internal table of addresses which tells the device which MAC addresses are on each interface. Once it has the interface identified, it sends the frame out that interface.