Blockchain at its core is simply a distributed ledger. Any transaction needs to be validated and verified. When you make a credit card purchase the card issuer validates that you have enough available credit and eventually transfer these funds to the seller. This is an example of a centralized ledger. The bank controls this information and controls the decision-making process. This is fine if the market always wants to rely on large expensive organizations to do this.
What if I am just a small website selling goods and I want to transact in a very cheap way that cuts out these people in the middle all taking a fee. I could earn more for myself and get paid instantly. This is what something like bitcoin can provide. The bitcoin network consists of individual nodes or miners processing these transactions for a very small fee paid to them in bitcoin. The distributed nature also makes this very secure as no one node has all the transaction data. They each process a block of the info and then when all blocks are processed the transaction is approved and money is transferred. There is no settlement process either so people get their money immediately. This allows for global scale transaction processing at low cost that’s also highly secure.