Once you have completed your helicopter or aeroplane training you may choose to convert onto a different aircraft. Many pilots convert so they can carry more passengers or to upgrade from a piston to a turbine engine aircraft.
You begin with ground school and will need to pass the accompanying written tech quiz before commencing practical training on the aircraft in question. Once deemed competent, an onsite examiner will conduct your practical flight skills test. If you are completing a multi-engine or Type rating, a designated flight examiner (DFE) will conduct the test.
The specific requirements for each rating will depend on the aircraft you choose to fly.