The first concept you need to understnad about the blockchain is the following. There isn’t one. There are many. Blockchains are distributed, tamper proof public ledgers of transactions.
Have a look at: What is The Blockchain Guide
If you still need some clarification on how it actually works. Don Tapscott is here to help, demystifying this world-changing, trust-building technology which, he says, represents nothing less than the second generation of the internet and holds the potential to transform money, business, government and society.