The main purpose of blockchain is to provide a secure and decentralized way of storing and sharing information or transactions between multiple parties without needing a trusted third party or intermediary. This is achieved using a distributed ledger that records verifiable and tamper-proof transactions, ensuring that no single party can control or manipulate the data. Blockchain technology is often associated with cryptocurrencies but has many potential applications in finance, supply chain management, voting, and more industries.

Blockchain is a distributed digital ledger that records transactions in a secure, transparent, and tamper-proof manner. It creates a decentralized network of computers known as nodes that maintain a copy of the ledger and validate transactions. Each block on the blockchain contains a set of transactions that the network's nodes have verified. Before a new block can be added to the chain, it must be validated by the network's nodes through a process known as consensus.

Consensus is achieved through a variety of mechanisms, including proof-of-work (PoW), proof-of-stake (PoS), and delegated proof-of-stake (DPoS). PoW is the most well-known mechanism used by cryptocurrencies such as Bitcoin and Ethereum. It involves solving complex mathematical equations to validate transactions and create new blocks. Once a block has been validated and added to the chain, it cannot be altered or deleted. This creates a permanent, immutable record of all transactions on the blockchain. The distributed nature of the blockchain also makes it highly secure, as any attempt to tamper with the ledger would require changing the records on every node in the network, making it virtually impossible to do so undetected.

The blockchain's ability to create a transparent, secure, and decentralized ledger has numerous applications beyond cryptocurrency, including supply chain management, voting systems, and identity verification.