Taking the bus from Venice Marco Polo Airport to Venice

ACTV bus is a commuter bus, makes a few stops.
ATVO is a tour coach, runs express, luggage is under floor.
All cost the same. No need to pre-book.

And there's a ticket booth in the terminal, where you can also get a vaporetto pass and save a little money with a combined bus/vaporetto ticket. Your bus destination in Piazzale Roma, the terminal at the end of the causeway which is the last stop for cars, trucks, and buses. From there on it's by foot or by boat.

The buses take you to Piazza Roma, just outside of old Venice. Then you take a vaporetta to your hotel stop.

Or use the Alilaguna , which is the airport water transportation into Venice, 15 €, various stops actually in Venice. We were just there in May. Check the schedule for the color- coded line closest to your hotel. Machines are throughout the airport from which to but tickets. Not sure you can buy tickets in advance, nor want to, not knowing if your plane is late, or how long passport control takes. For our past May trip, passport control, in the evening, took a mere minutes. Signage is clear, directing you to the Alalugana dock.

Safe travels!

For something very unique consider taking the water taxi ferry system. It picks up at the Venice airport and goes through some other island towns like Burano and makes it's way to the Grand Canal in Venice dropping off close to the main square. I have taken it from Venice to the airport and loved every minute of it. It is public transportation so probably will cost about as much as the bus would but the view and introduction to Venice would be amazing for you.

https://www.alilaguna.it/en/lines/lines-map

Ask your hotel which line and which stop to use .
Safe travels!

Water transport in Venice.
1. Gondolas. Only for pleasure, not for transport.
2. Traghetto – big gondolas, two oarsmen, about ten passengers, for crossing the Grand Canal. Found at Rialto, San Toma and a couple of other places.
3. Water taxis, which are like a floating limo, costs to match.
4. Vaporettos - ACTV. Are waterbuses, operate on a bunch of routes. Get the app Chebateo for routes and schedules. Vaps do not service the airport. Vaps are not water taxis.
5. Alilaguna ferries, service the airport, run from Marco Polo via a bunch of stops to the main part of Venice, Murano and Lido. They stop at some, but by no means all, vaporetto stops.

Although vaporetti are the Venetian equivalent of city buses (they just run on water rather than roads), they are not priced like city buses. A single-ride ticket costs 9.50 euros. It's worth thinking about how much you may choose to ride rather than walk, because there are vaporetto passes that might save you money. A 24-hour pass costs 25 euros; 48-hour pass, 35 euros; 72-hour pass, 45 euros; one-week (168-hour) pass, 65 euros. A pass is cheaper for young folks and students.

Walking is a great way to see Venice, but you'll need water transportation if you want to go to Giudecca, San Giorgio Maggiore, Murano, Burano, Torcello or the Lido, and most visitors want to take at least one ride down the Grand Canal. Depending on where your hotel is, you may also want to take vaporetti on the way to and from your hotel.