Development began in 1984 at Beijing Language and Culture University and in 1992 the HSK was officially made a national standardized test. By 2005, over 120 countries had participated as regular host sites and the tests had been taken around 100 million times (including by domestic ethnic minority candidates).The general count outside of China is stated as being around 1.9 million. In 2011 Beijing International Chinese College became the first HSK testing center to conduct online HSK test.

The HSK test approximates the English TOEFL, and an HSK certificate is valid without any limitation in The People's Republic of China. The test aims to be a certificate oflanguage proficiency for higher educational and professional purposes.

Each year HSK certificates are issued to those who meet required scores. The HSK is administered in Simplified Chinese. In addition test takers with outstanding results can win a scholarship for short-term language study in China.
From http://en.wikipedia.org/wiki/Hanyu_Shuiping_Kaoshi
 
 
The number one reason is that Mandarin Chinese is the most widely-spoken language in the world. Learn to speak Mandarin and you can speak with millions of people around the world. More reasons:

  • Business - Business people who speak Mandarin have a huge advantage in tapping into the Chinese market. It is much easier to develop all-important relationships if you can speak Mandarin.
  • Travel - China and Taiwan offer exciting travel opportunities. Getting around is much easier if you can speak Mandarin.
  • Culture - With thousands of years of history, Chinese culture is endlessly fascinating. Whether your interests are in history, architecture, music, or cuisine, a knowledge of Mandarin will enrich your understanding of Chinese culture.
  • from About.com
 
 

Sharing some Pinyin Tutorial from Youtube.