To take advantage of these prices you will need to prove you are a leisure traveller, on the way to stansted airport, so you will need to provide either your flight numbers or yr holiday booking reference. I don't think you will need to give this when you arrive at the station but you may be asked to give them on yr travels from the station to the airport.
Going to the airport by train is great, you can take a nap, read (even at night), play a game, or just gaze out of the window... The other restriction to buying these inexpensive train tickets from vauxhall station to the airport is that there must be at least two grown ups travelling together. But another great benefit is that children go free. All children under five go free, and then one child over 5 but under sixteen per grown up travelling by train to the airport.
be sure to leave plenty of time to get to stansted airport early enough to eat, shop etc, so check the times of trains from vauxhall station before you go. If you have time to kill at the airport you can always read a book or play a game again! As you have bought your train ticket in advance, you don't need to worry about the opening hours of vauxhall station.
Or maybe you meant