The car is always automatically insured by the car hire company.You don't do anything.You have no choice but to have that insurance.The hire company will refuse you the car if you are outside their policy e.g a very young driver .You will be offered extra insurances. These are for such things as personal injury to yourself and passengers, theft of goods from the vehicle and, most significantly, 'collision damage waiver'. This is the CDW referred to above. When you hire the car you are liable for all damage it suffers, up to some financial limit, usually rather high. If you take the CDW your liability is reduced to a much lower figure. You should check the car before driving off , to make sure that there is no damage to it which the company has not recorded on the hire document. Most companies provide a diagram of a car with the damage marked on it in addition to a description of the damage. If existing damage is not noted or reported by you the company will treat it as damage occurring during your hiring.