To Buy an Oyster card online:
Visit this link to get your oyster card online (Get Oyster Online).
Now you will see a box stating “Get an Oyster card”, from this box select “Order a card online”.
Now select “Pay as you Go from the options you are presented with”.
After that you have to select the amount of balance you want to load on your oyster card. After selecting the amount, click on continue. Now you will be able to see your basket. Make sure that you have been charged with 5 pounds of refundable security deposit along with the amount you have added on.
After assuring that order is correct, select your preferred method for delivery. You have a free option or you can use express delivery option for 4.60 pounds and then click on continue.
Now you will be presented by disclaimer instructions. Read them with keen care and agree to them before clicking continue.
Now you will be presented by an option to enter security question. Select a security question and then enter your desired security answer. Now click Continue.
Now review your order again and fill out the payment page. Accept provided terms and conditions and click on button to continue.
It is all done now; your oyster card will be with you in time frame provided by TFL.
Buy Oyster card at a Station
Go to any of the London train or tube stations and locate the ticket shop.
Talk to the customer service representative there that you want to buy pay as you go oyster card and tell him the amount you want to add on it.
You will be charged with 3 pounds security deposit and the amount of balance you want to add. Representative will tell you the instructions to use the card.