ELI5: What is blockchain?

Imagine you and your friends love playing with LEGOs. You all want to keep track of who owns which LEGO set.

Instead of relying on just one person's memory (which can be wrong!), you decide to create a special notebook. This notebook is called a blockchain.

Here's how it works:

1. Sharing the Notebook: Everyone gets a copy of the notebook. If someone wants to trade a LEGO set, like "Alice trades her spaceship to Bob", it's written down in the notebook.

1. Adding a Block: Every time a few trades happen, they are grouped together into a page, which we call a block.

1. Securing the Block: Before adding a new page (block), you use a special secret code (like a password, but much harder to guess) based on everything written on the previous page. We can call this code a hash. This means that if anyone tries to change something on a previous page, the secret code won't match, and everyone will know someone is cheating!

1. Sharing the New Block: Once you've created the new page (block) with the secret code, you show it to everyone. Your friends check if the secret code is correct and if the trade is valid. If everyone agrees, they all add the new page to their notebook.

1. The Chain: Each new page (block) is linked to the page before it using the secret code. This creates a chain of pages – that's where the name "blockchain" comes from!