Hong kong Visit

Hello Guys,

 I am planning to visit HK in April for 3 days only. Could you please suggest me where to go (must see place in HK), and also any budget hotel to stay for 3 nights?

Any pass to commute in buses and trains? Where to shop? And what to buy? As I dont know anything about HK. 

Any other suggestion or help are really appreciated.

Thank you.