Why Use The Underground in London? The underground (or tube) is in most cases the fastest way of getting around in and across London. And it is not that expensive compared to taxi and driving own car with congestion charges in Central London
How Much Does it Cost With The London Underground? This depends where you are going and from where. The london-underground is divided into zones, where Central London is 1 and 2, the further out (or in, depending on where you are) the more it cost. But for a one-way tube journey the cost is around £4. It is recommended to either buy a day-travel card - if you are staying just one day, or a Oyster-card if you are staying for several days.
What is an Oyster-card and How Much Does it Cost? An Oyster-card is a pre-pay card for using on public transport in London, with this card you do not have to queue up for buying tickets, you only touch the card in the turnstile and enter the train. The cost of the oyster-card is a £5 deposit, which you get back when you hand it in. And then you can either top it up with as much money as you need, or buy a travelcard (daily, weekely, monthly etc.)
Where do I Buy Tube- and Oyster-Card tickets? Some kiosks, off-licenses and such sell paper tickets, but to buy an Oyster-card you have to buy it at one of the Underground stations in London.