what is the difference between pay as you go and travelcard oyster?
A paper travelcard is less fancy. If you don't travel a lot (i.e. take only 1-2 rides on some days) then you may want to get an Oyster card that operates as Pay As You Go (PAYG). Oyster PAYG works just like a charge card, you put money on the card and an amount is deducted every time you travel.