If they are based at the airoprt they will be grouped together with the others on a lot on the airport approach road. If you have pre-booked they will pick you up at arrivals and take you there, if not it's a bit of a hike to the lot.
If you are staying on the Kasandra peninsular I suggest you hire a car from Kriopigi Cars, great prices, great people and they will pick you up at the airport.