How do I use an Oyster card on the Tube/DLR/London Overground/trains?
You enter any station by touching the card on the yellow Oyster card reader. The gate then opens, to let one person in. It will only open once. To exit a station you must always touch out. Again the gate will only open once. This of course also means you can only be charged once. See FAQ 37 for an exception.