The Vigene`re cipher

In relations to the book “Simon Singh, The Code Book; The Secrets Behind Codebreaking” What is The Vigene`re cipher? Why is this code is hard to break? Are there an advantage to this type of cryptology? The chapter starts on page 51 of this file you can find on the internet. http://index-of.co.uk/Hacking-Coleccion/164%20-%20The%20Code%20Book%20How%20To%20Make%20It,%20Break%20It,%20Hack%20It,%20Crack%20It%20%5B-PUNISHER-%5D.pdf