Typically found in a basement, pull chain fixtures are used all over older homes. They are prone to failure from excess pulling, (got kids in the house?) However, they wear out just like everything mechanical.
This video shows color coding between the 4 wires and screws. It’s quite simple really, a white wire will go to white metal or a silver screw, and the black wire will go to a brass or the darker screw.
White to white metal, black to brass metal. White to white, black to brass.
It is called polarity, the silver (zinc colored) screw connects to the threaded portion of the lamp socket and the brass screw connects to the switch and the bottom center terminal of the socket.
This provides some safety to the fixture as when you are screwing in a bulb, your hand can touch the threaded portion of the bulb and, if wired correctly, will be the neutral leg of the circuit and not able to give you a shock.
The black wire is disabled by the switch, a good safety feature, and then feeds the bottom contact in the socket, the hardest to touch when changing a bulb.
THIS IS HOW THINGS ARE SUPPOSED TO BE WIRED. NEVER TRUST ANY ELECTRICITY DUE TO THE POSSIBILITY THAT A PRIOR HANDYMAN MAY HAVE MISS-WIRED A CIRCUIT – IT COULD BE FATAL!!