These are massive single pole - double throw (SPDT) sealed relays. This means that when current is applied to the coil it throws a simple changeover switch, terminating the connection from the NC contact to ground and closing the NO contact. Use them to switch high voltage/high current devices.
This relay’s coil is rated up to 12V, with a minimum switching voltage of 5V. The contacts are rated up to 5A (@250VAC, 30VDC).
This particular SSR can switch current loads of up to 40A with a 3-32V DC input and a zero cross trigger control method. Each one of these relays is equipped with four screw terminals (for use with ring or fork connectors) and a plastic cover that slides over the top of the relay to protect the terminals.