This device has a PC female socket upon its side, a "cold" flash shoe upon the top and a button upon the bottom. When this device is placed into a "hot" flash shoe of a camera, firing the camera will activate anything connected to the PC female socket upon the side.
Use a cord with a "PC male" connection upon one end and whatever your flash employs to fire upon the other end, insert the PC male connection of the cord into this device and the other end of the cord into the flash. When the camera fires, assuming this device has been placed in the hot shoe of that camera, your flash connected to this device's PC female socket will also fire.