From the airport, you can take the express bus to Piazzale Roma. The cost is 8 euro per person. Piazzale Roma is the end of the line for land vehicles in Venice, it’s all by foot or boat from here. At Piazzale Roma, you can take the Vaporetto, which is the public water transportation system in Venice. A ticket good for 75 minutes will cost 7.5 euro, although they do have a variety of multi-day tickets available if you think you will use the system often. You will want Line 1 or 2, and will get off at the San Marco Terminal. Your hotel should be no more than a 10-minute walk although I would reach out to your hotel for specific walking directions as it’s easy to get lost in Venice.
There is another service called the Alilaguna Water bus that goes directly from the airport. It takes over an hour and crosses the lagoon to get out to Venice. The cost is about the same as the bus/Vaporetto and it does stop at the San Marco Terminal. At the airport, it’s about a 10-minute walk to the dock.