There are several other threads on this topic (some about reversing cameras) which may help you. Assuming you have a caravan you have a choice of wired or wireless connection between camaera on back of caravan and monitor in car. Wireless is good and easier to install with no problems of connectors out in the wet.
Somewhere like www.parkingcamers.co.uk have a good selection and offer advice.
My choice is for a monitor which fits over the driving morror. This is the instinctive place to look when driving and is shaded from the glare which can affect dash mounted monitors. Many cameras have infra red emitters which 'illuminate' to the rear - great in the dark or in tunnels.
The camera has a transmitter which requires a 12v supply. You will need to take this from the battery as the caravan 12v. circuits apart from fridge are disabled when connected to car and engine running. The receiver can be most anywhere in the car and also requires 12v supply usually by plugging in to one of the ignition controlled 12v sockets now fitted to most cars. In my Freelander there is a convenient point in the rear loadspace which is ideal.
In my opinion this is the best single add-on after a motor mover particularly when towing in Europe.