#2 Simple Structure of Blockchain

A blockchain is simply a shared ledger that holds transactions and every  transactions fits in a block  which is of following structure

a) Previous Hash  : A Hashpointer that points to previous block ,its null if its genesis block(starting block).

b)Transactions : List of transactions that pertains to current block.

This is generic structure that is used upon various blockchains like bitcoin,ethereum, but they use various parameters along with transactions which would be listed separately in other post.