The majority of new cars that are purchased do not come with a tow bar fitted as standard so if you need to tow a trailer or caravan you will need to have one fitted or source a used car which has a tow bar already fixed in place.
There are two options open to you should you find that you need this addition to your vehicle the first is to buy the tow bar and a fixing kit and fit it yourself or to employ a company to do this for you. It is obviously cheaper to fit the tow bar yourself, but it is not an easy task and certainly should not be attempted unless you have some mechanical engineering knowledge. The forces involved in towing a caravan or heavy trailer mean that the tow bar is under a lot of pressure so will need to be bolted to the chassis of the car.
Probably the wisest choice would be to make enquiries into companies that fit tow bars and the various types available. For instance, a cheaper option is to have a tow bar that is permanently in place rather than one that can be detached when not in use.