Blockchain technology offers society a new capability: sharing business records whose tamper resistance can be trusted more, and for a longer duration, than any of the participants trust each other. This capability expands the reach of useful constructs that were previously limited by trust boundaries, such as digital money, smart contracting, and many others.
The attached animation summarizes how they work. New user data is collected, and then a "fingerprint" (cryptographic hash) is created to summarize the collection. That fingerprint is then combined with a fingerprint of the prior block to create a new block. The resulting chain of blocks creates a tamper-resistant structure where no historical record can be changed without disrupting every subsequent block hash, thus consolidating the problem of tamper resistance down to the problem of securing the most recent block.
This animation does not explain how the most recent block is secured. Traditionally, this employs "Proof of Work", wasting over $2 billion annually in electricity. Some chains are attempting Proof of Stake. Some just use old-fashioned trusted custodianship in disguise, defeating the very point of blockchains. But there is a better way!