Blocks are batches with a seal

A single transaction is a line in a notebook. A block is a numbered page of those lines, plus a fingerprint of the page before it. That pointer is why people say “chain.” Change an old page and every later fingerprint stops matching.

On Ethereum a new block is proposed about every 12 seconds. Each block has a parent, a list of transactions, and a state root — a compact fingerprint of every balance and contract after those transactions run. You do not need to understand the cryptography. You need the picture: history is append-only and public.

The fingerprint in these lessons is a toy hash, so you can see the idea. Real Ethereum uses cryptographic hashes that are impractical to fake. Explorers like Etherscan are just searchable views of the same public data.

Queue a few transfers, seal a block, then seal another. Notice how each new block names the one before it. That is the whole trick, drawn small.