To add a vehicle, simply click on the green "+" button in the "Garage" tab. A dialog will then prompt you for the following details of the vehicle you wish to add: Year, Make, Model, License Plate, and optionally, a picture of the vehicle. If it's an Electric Vehicle, you should check the "Electric Vehicle" switch. This ensures that "fuel" economy is measured in kWh instead of gallons or liters.
To delete an existing vehicle, click on the "Manage Vehicle" dropdown and select "Delete Vehicle". You will then be prompted for confirmation before the vehicle is deleted. Once the vehicle is deleted, you will be redirected back to the Garage.