How does public transport work?
There are plenty of ways to get around Hong Kong, whether by taxi, ferry, train, bus or tram. The city claims one of the world’s safest and most efficient public transport systems and a convenient payment method in the form of the Octopus card.
You can find the route planner of the Hong Kong Transport Department here.
To use public transport without cash, you will need an Octopus card. There are various types of Octopus cards available while Sold Tourist Octopus may be the best choice for tourists as it provides great convenience to you for both transportation and retail purchases during your stay in Hong Kong. This Octopus has some Hong Kong iconic landmarks featured on the card face, and you can easily get it from the major convenience stores within the airport or city.
(Source: http://www.tripadvisor.com/Travel-g294217-s303/Hong-Kong:China:Public.Transportation.html)