Hash functions are used to create new blocks and link them to the previous block, forming a chain of blocks, hence the name blockchain. Here's how:

1. A new block is created and filled with transaction data.

2. The block's header is hashed using a hash function like SHA-256.

3. The resulting hash value is included in the block's header.

4. The block's header also includes the hash value of the previous block's header (the "previous block hash").

5. This creates a chain of blocks, where each block is linked to the previous block through the previous block hash.

6. The blockchain is updated by adding the new block to the end of the chain.

This process:

- Creates a permanent and unalterable record of transactions.

- Ensures the integrity of the blockchain, as any changes to a block would result in a different hash value.

- Enables the creation of a decentralized, trustless, and censorship-resistant ledger.

By using hash functions to link blocks, blockchain technology ensures the security, transparency, and immutability of the blockchain, making it a robust and reliable way to store and verify data.