The Airport Express is built in to the front of the airport terminal building – you don’t need to go outside – and is very well sign posted from inside the terminal.
There are no staffs on the trains and you can either buy tickets before you board, at the manned or automated ticket machines, or just get straight on the train and pay at the counter at the other end.
Usefully that means you can jump of the first train that pulls in to the station.
Trains are modern with air conditioning and plenty of luggage space and there is almost always a seat. Unfortunately, you won’t get much of a view. While you get a look across the rural backyard that is Lantau Island when the train first pulls out of the airport it quickly enters a tunnel to reach Kowloon and Hong Kong Island.