Brake controller
Any trailer weighing over 750kg must have independent brakes. Some trailers employ a mechanical system where the hitch moves in and out and applies the brakes, but most these days use electronic brakes which are controlled by the vehicle doing the towing - through a brake controller device.
Before you set off, take the time to learn how to adjust the brake controller settings so you have the right amount of braking for the trailer load. And make sure you know how to activate the emergency stop feature.