Question: [The Wikipedia article on Korea](https://en.wikipedia.org/wiki/Korea) states that South Koreans call Korea 한국, while north Koreans call it 조선. Do 'Korea', '한국', and '조선' all refer to the same thing? If so, how did the three different names come about?

Answer: 
Basically, 'Chosun' is the old name of 'Korea'. Used a lot in the past, it is rarely used anymore. 'North Korea' still uses the term 'Chosun', but it is rarely used in South Korea. That's why you have to understand the two words differently.
The English word "Korea" comes from the Korean word Koryeo (고려 / 高麗). Koryeo is a historical dynasty existing between 918 and 1392. As such, it does not make much sense to modern Koreans as a name for their country.