You can register a vehicle as either a finance or a security interest. To do this simple hover over the 'registrations' item and select the type of interest you'd like to add. There are 4 pieces of information you can add:
The VRM of the vehicle you want to add the interest to
The VIN of the vehicle. This should be the full 17 digit VIN. You should never use the shortened VIN when registering an interest.
This is an optional field, allowing you to enter the mileage of the vehicle.
This can be anything to help you find this vehicle again in the future. For finance interests, it could be the finance agreement reference.