Blockchain is based on a decentralized ledger that can lessen costs by withdrawing the intermediaries such as banks and by creating the effective decentralizing trust between the organizations and customers. The blockchain supplements the entries to the ledger which are formalized by the wider user-community rather than by a central authority.
Each block stands for a transactional record and the chains that are linked with them. The blockchain sustains the records distributed among computer networks and lists the blocks of transactions sequentially. For the further understanding, read carefully the given picture below.
Bitcoin is a good example to understand why the “blockchain” is considered too secure. In Bitcoin’s blockchain, the shared data is the history of every Bitcoin transaction ever made. You can also say it’s just like an accounting ledger. The ledger is stored in multiple copies on a network of computers, called “nodes.”
For the confirmation of transactions validity nodes are being checked each time when someone submits a transaction to the ledger. A subset of them compete to package valid transactions into “blocks” and add them to a chain of previous ones. The owners of these nodes are called miners. The people who makes the addition of new blocks profitably will be able to earn bitcoins as a reward and knows as minors.