OYSTER CARD HELP please !?

You can buy a 'pay as you go' Oyster Card from the Transport for London (tfl) website. You can then either top it up online or top it up on your next trip to London, it is cheaper than a travel card and easy to use, plus if you ever have under 11's travelling with you four of them go free on the tube with every Oyster Card holder so ideal for families.