Think of a simple notebook, or a ledger, where you keep track of transactions. Every time you spend or receive money, you write it down. This notebook is a central record. If you lose it, the record is gone. If someone changes an entry, it might be hard to prove what the original was.

A blockchain is like that notebook, but it’s digital and shared across many computers. Instead of one person holding the master copy, everyone in the network has an identical version. This setup makes it incredibly secure and reliable. Its main purpose is to record information, whether it's financial transactions or other types of data, in a way that is very difficult to change, cheat, or hack.

The name “blockchain” gives a big clue about how it works. It’s a chain of blocks. Let's break that down.

Each block also contains two other important pieces of information: its own unique identifier, called a hash, and the hash of the block that came before it.

This is how the chain is formed. Each new block points back to the previous one by including its hash. This creates a secure, interconnected line of blocks, starting from the very first one, often called the Genesis Block.

This structure is what makes a blockchain so secure. If someone wanted to alter the data in an old block, they would change that block's hash. Because the next block in the chain contains the original hash, the link would break. To successfully change a block, a person would have to alter that block and every single block that comes after it, all across the network, which is practically impossible.

The structure of a blockchain gives it three powerful characteristics that set it apart from traditional databases.

Together, these features create a robust and trustworthy way to record and share information. Now that you understand the basic building blocks, you're ready to explore what this technology can do.

Let's review these core concepts.