Since this is a very general question, I will answer it to a very general audience. Blockchain is just a way of storing data. And it’s stored in such a way that basically when something has been added to the blockchain (a transaction, a word, or whatever you are storing) has been added to it, there is no way to change it. If you change anything in the preceding data, then I will be able to see it today.
"If you have a traditional database, you could modify a single entry, and no one would know. But the way a blockchain is structured, if you change even the tiniest detail, everyone would be able to track it."
You should care about it because it opens up a bunch of very interesting applications. You can have a voting system, for example, which everyone can verify, which is not possible with traditional modes of storing data because you can modify them. If you have a traditional database, you could modify a single entry, and no one would know. But the way a blockchain is structured, if you change even the tiniest detail, everyone would be able to track that this blockchain is not valid anymore. So that’s what makes it special.