How would you explain the difference between a state, country and continent?
Sometimes "state," "country," and "nation" mean the same thing. When we in the US refer to the Secretary of State, we are referring to the person who represents the country when dealing with other nations.
In the US, "state" refers to one of the 50 units that make up the country. Each state has its own government. To us, the word "country" also means nation, comprised of all 50 states.
A continent is a very large land mass which usually includes several or many nations:
http://en.wikipedia.org/wiki/Continent
Australia is the only continent which is also a nation or country.