The system is easy to follow and anyone can use it easy, even foreigners with no English would find it easy to follow as the lines are all different colors. When the tube is running, it is really convenient and easy to use, and if you get the Oyster card, quite a bargain.The Oyster card is definitely worth getting as the price is nearly 50% of the regular rate.Many will have a long-term travel pass attached to the Oyster, and these can be valid for as short as a week or as long as a year.
You can use Oyster or Contactless payment cards on the trains to/from Gatwick Airport but it may well be cheaper to buy tickets from the railways instead.
The Contactless payment card is the new option available and the authorities hope this may become the dominant channel in the longer term.
However for short-term visitors the adoption rate is far less and for good reason, especially if you are from overseas and do not have a British sterling or pound currency credit/debit card.
I can not stress to you the importance of registering your Oyster card. I lost mine but luckily had the receipt with the card serial number on so I was able to get it cancelled and the balance transferred to my replacement.
They are supposed to tell you to register it when you buy it but the cashier didn't. It runs on time to the the second, gets a person where you want to be in no time, without the hassles of congested traffic you would find going by car, and much quicker as well as it moves in a direct line, the staff at the ticket points were always efficient and courteous.