I will stay 2 days in Hong Kong. Something about the Octopus Card

If you want to take the mtr and the light rail for unlimited times, you need to buy the airport travel pass or Tourist Cross-boundary Travel Pass.
But the Tourist Cross-boundary Travel Pass cannot be recharged and used as the common Octopus card. The airport travel pass can be used as the octopus card if you recharge it.

The ordinary octopus card can only be used on star ferries and buses, but cannot be used on the Tram and Peak Trams.

The price depends on where you start your journey. It is har do tell without any other detail information.