If the trailer has electric brakes you need a brake controller. It mounts to your tow vehicle and provides electrical current to the trailer brakes to activate them. They are set up so that the quicker the stop, the harder the trailer brakes activate. Check out etrailer for info and suggestions. And yes, there should be a brakeaway cable. It attaches to your tow vehicle and activates the trailer brakes in the event the trailer becomes separated from the tow vehicle.
Your trailer might have surge brakes which operate differently. They are hydraulic and activate when the tow vehicle slows down and the trailers pushing on the tow vehicle activates them. They will have something similar to a cars master brake cylinder.