I’ll paste what I wrote in
https://cryptologie.net/#article_555The simplest abstraction is to see cryptocurrency / blockchain / distributed ledger technology as a database running on a single computer. Everybody can access this database and there’s some simple logic that allows you to debit your account and credit someone else’s account. The computer has a queue to make sure transactions are processed in order.
Blockchains that support smart contracts allow for people to install programs to that computer, which will add a bit more logic than simply debiting/crediting accounts. Others can then just send transactions to this computer to make a function call to any program (smart contract) that was installed on the computer.
The cool thing really is that we’re all using the same computer with the same database and the same programs.
Now in practice, nobody would trust a single point of failure like that. What if the computer crashes, or burns in a fire? Distributed systems to the rescue! We use distributed system protocols to run the same database on many computers distributed around the world. These distributed system protocols effectively simulate a single database/computer so that a few computers failing doesn’t mean the end of the blockchain.
On top of that, we refuse to trust the computers that participate in this protocol. They could be lying about the balance in your account. We want the computers to police one another and agree on the database they are simulating. That’s where consensus protocols are used: to make the distributed database secure even when some of the participants are malicious.
And that’s it. That’s blockchain tech for you. The obvious application is money, as the secure and simulated single computer is useful to simplify a payment system, but really any distributed database that cannot trust some of its participants can benefit from the advances there.