There really are two ways to get to Ca D’Oro Hotel from Marco Polo Airport. You can take the Alilaguna Water Service, Blue Line, directly from the airport to the Fondamente Nove Terminal. Your hotel is about a 5-minute walk from there. If the weather is nice it can be a pleasant trip across the lagoon, however, it will take about an hour. The other option is to take the bus or a taxi from the airport to Piazzale Roma, which is the end of the line for land vehicles in Venice. From Piazzale Roma you would hop on the Vaporetto (Line 1) and get off at the Ca D’Oro Terminal. Your hotel is just a few minutes from the ferry stop. With this option you get to ride down the Grand Canal for a bit, which would be a nice introduction to Venice.
The two options cost about the same and both take some time. With the bus/taxi to Vaporetto option you have the transfer at Piazzale Roma. With the Alilaguna you have no transfer but a longer boat ride across the lagoon, which if the weather is bad might be a rough ride. Bottom line is either option gets you where you’re going.