When you arrive at the airport, follow signs for Long Stay car parks 2 or 3. You can also park in car park 4 with this package.
Pull up to the entrance barrier and press the button for a ticket. You'll need to keep this safe, as the car park's people will validate it on your return so you can exit the car park. Then just pull into any one of the parking bays and walk across to the terminal. You can take your keys with you, as your car will stay where you left it while you're away.