(Chinese version available here, courtesy of @jiangplus
(This is an English translation of my Danish blog post, Bitcoin for voksne)
Bitcoin is a digital currency that has no central authority. It's a currency where you do not have to rely on anyone to know it's worth it. As a concept, it's similar to gold. Gold has a value in itself, as opposed to, say a $100 note that only has value if the U.S. government says it has value. Similarly, the idea of Bitcoins is that they have value by themselves.
Let's try to understand how Bitcoin works.