Your Vehicle Details are generally auto-populated for you when entering the vehicle registration. Although auto-populated, they are changeable if you so wish. The vehicle details section covers the vehicle's basic information such as make, model, transmission type right through to colour and upholstery type.
There may be cases when you'll need to enter these fully-manually.
Typically when adding a vehicle by registration you will only need to input the mileage before saving and moving to the next section.