Today this post for Block chain.
I introduce Block chain simple concept and a few reference.
First, What is Block chain?
Simple concept, Block chain is distributed storage.
But that is guaranteed about all transaction.
You can be found at below for detail information.
Concept Block chain
https://en.wikipedia.org/wiki/Block_chain_(database)
How can use Block chain? for developer
How can you understand
https://blockchain.info/ko/api
Finally, open Block chain