Turn on CNBC or any business/ financial news channel today and you're likely to hear about Bitcoin. Blockchain is the technology behind Bitcoin and all cryptocurrencies. If you're not familiar with how blockchain works or you're looking for a simple explanation to share with your students, Common Craft has you covered. Blockchain Explained by Common Craft makes a great analogy between keeping a ledger of tangible assets to keeping a ledger of digital assets. The presentation of that analogy makes it easy to understand how blockchain works.
Once you understand the basics of blockchain you might want to learn more about cryptocurrencies. Blockchain and Money is an open course from MIT. The course was originally taught in the fall of 2018, but all of the materials and lectures are still available for free. All twenty-three lectures in the course can be viewed in this YouTube playlist. It is a graduate course so I don't expect that high school students would be able to understand all of it, but an interested high school student could still glean some good lessons from it.
Disclosure: I have a long-standing in-kind relationship with Common Craft.