Bridges :- Bridges are used to connect two separate LANs. LANs may be similar (Both LANs running same protocol like CSMA/CD)or dissimilar(like one LAN running CSMA/CD and other running Token ring).
Bridge acts as bridge to connect two LANs.They regenerate signal like repeater but not mindless like repeater , they works on MAC address. Like suppose your college campus is at two places (campus 1 and campus 2). Now to connect computer science department of campus1 to computer science department of campus2 directly , use bridge.