A "kind" is a type of something, a family of sorts - related to the word "kin". So "one of a kind" means you are the only example - you're the only one of a kin(d)!

UNIQUE

A.I.: "You are the first of a kind." :)

I remember this question has been asked before. http://www.italki.com/answers/question/36351.htm

It means you are special, that nobody else is like you.