Suppose you want to transfer 1 lakh rupees to a friend. There are two ways to do it 1) give your friend cash or 2) transfer it through a bank. In either situation, the bank overlooks your transactions in a direct or an indirect way. How about we eliminate the authority and provide a decentralized system where there’s no single authority to overlook your transactions?
That’s the general aim of Bitcoin – to eliminate the authority and provide a decentralized system.
So, what is this term called Blockchain?
Even after you eliminate authority, you need some sort of verification for transactions. Suppose you have ten apples and you give me five, how can show proof to the third person (like income tax, for example) that I only have five apples? You need some sort of receipt and a legitimate proof that transaction occurred, right? This is where Blockchain comes in.
The blockchain is nothing but a chain of systems operating on the Internet that verifies transactions. Think of creating a document to record transactions in your Google drive which is shared with a group of users that update the document with transactions as we go. This is a blockchain.
How does this all fit in?
Suppose you transfer 10 Bitcoins from your Bitcoin wallet to a friend, you both and the system in the Blockchain gets a transaction ID and a receipt that the transfer occurred.
Blockchain in Bitcoin doesn’t store your personal details except for the verification of transaction and the transaction ID so there’s no way for Blockchain to modify any transactional data it gets. In short, you can’t manipulate the Blockchain.