The United States of America (USA), commonly known as the United States (U.S.) or America, is a federal constitutional republic made up of 50 states and one federal district- Washington D. C, the capital district. The U.S is the center of global trade and the world's largest economy with the most prestigious universities in the world there.  

Weather
Summer: June to August from (25°C to 35°C)
Fall: September to November (from 10°C to 18-21°C)
Winter: December to February (from -4°C to 7°C)
Spring: March to May (from 7°C to 15°C)
http://www.worldweather.org/en/home.html

Clothing
Summer: Sweatshirts, T-shirts, shorts, a light jacket
Fall: Light sweaters, hoodies, rain jacket, a light scarf
Winter: Lots of layers! Winter coat, gloves, scarves, winter boots
Spring: Raincoat, rainboots, light fleece jacket, T-shirts

Capital
Washington, D.C.

Language
There is no official language in the U.S., but English is the most commonly used language.

Power Plug
Type A & B: The standard voltage is 120V and the standard frequency is 60Hz.
https://www.worldstandards.eu/electricity/plugs-and-sockets

Time Difference
The U.S. has a total of nine time zones.
Summer time (late April - early October):  12-20 hours behind Hong Kong
Winter time (late October - early April):  13-21 hours behind Hong Kong

Currency and Exchange Rate
The United States Dollar (USD) is used here and notes come in denominations of $1, $2, $5, $10, $20, $50 and $100. Coins come in 1¢, 5¢, 10¢, 25¢, 50¢ and $1.00. The United States Dollar (USD) Around 100 HKD = 12.8 USD

Visa Information
Holders of HKSAR passport (with at least 6 months of validity) are required to apply for visas to enter the US. In general, foreign citizens of the US must obtain a temporary stay of non-immigrant visa or permanent resident immigrant visa.

Useful Numbers
Police, Fire & Ambulance:  911

Funny Facts about the U.S.
i) Many people interested in technology head to Silicon Valley from all around the world.
ii) Virginia has birthed more presidents than any other state.
iii) Harvard was the first university in the United States.