Couldn't be easier. At the airport, there is a booth where you can get info on transport. They speak great English. You can buy tickets there for the local buses which will take you the few miles to Venice. From memory, the local bus service (yellow No.5) bus is more for locals and has little room for luggage. The blue ones (ATVO flybus) are more touristy and are quite cheap, about 3 Euros. They both leave from just outside the door. Problem with Venice is that cars and buses can only go as far as Piazalle Roma where they all have to stop and park or turn round. You can go from there to the nearby vaporetto (waterbus) station and get to virtually anywhere in next to no time. You'll love it. I went there last year for the first time and found the transport really easy and the place is out of this world.