Hong Kong is a coastal city on the south-east edge of China. The weather is pretty humid, summer being 70-100 F and winter being 50-70 F. The local language is Cantonese, not Mandarin Chinese. Signs are typically in traditional Chinese with English in the central areas. English is spoken by the younger generation. HK is a very dense city, with a lot of steep hills and tight spaces. The 3 main areas are Hong Kong Island, Kowloon, and New Territories.
If you don't have an international phone plan, it's easy to pick up a local SIM card at any 7/11 around the city. Transportation is through taxis, buses/mini-buses, or the MTR subway system. For public transit, get an Octopus card to tap in and out (Octopus card balances can be used for shopping at many supermarkets and stores as well). Arrange HKD in cash, as not everywhere accepts credit cards.