Depending on the country, the international driving licence may be free or for a small fee. In all cases, allow a reasonable period of at least 1 month to obtain it.
The international driving licence, valid for 3 years, is a translation of your English driving licence and is recommended but not compulsory.
It is in no way a substitute for your national driving licence, which you will still need to show on the day you pick up your car, and to the local authorities if you have to deal with them.