When you want to begin to understand how circuits work, where do you start?

It's totally fine to just build circuits and not really know why they work. I did that for a long time. And it's a lot of fun!

But if you want to start understanding the circuits, here's the first step:

Understand how voltage and current act in a circuit.

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There's no need to understand what is going on at a particle level. A lot of books and beginner course start there - which is very strange to me