using octopus card in MTR in HK

It is very easy to use it. You just put the card in front of the yellow Octopus readers and the machine will deduct the correct amount of money, when you take the mtr, ferries and public buses.
Once you get the octopus, you can do need to go to the both to get a mtr ticket, because the octopus can be used to take the mtr. The card readers can be found at the mtr stations.